sed, a stream editor
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sed, a stream editor
This file documents version 4.1.4 of
GNU
sed
, a stream editor.
Copyright © 1998, 1999, 2001, 2002, 2003, 2004 Free
Software Foundation, Inc.
This document is released under the terms of the
GNU
Free
Documentation License as published by the Free Software Foundation;
either version 1.1, or (at your option) any later version.
You should have received a copy of the
GNU
Free Documentation
License along with
GNU
sed
; see the file
COPYING.DOC
.
If not, write to the Free Software Foundation, 59 Temple Place - Suite
330, Boston, MA 02111-1307, USA.
There are no Cover Texts and no Invariant Sections; this text, along
with its equivalent in the printed manual, constitutes the Title Page.
#Introduction
Introduction
:                Introduction
#Invoking-sed
Invoking sed
:                Invocation
#sed-Programs
sed Programs
:
sed
programs
#Examples
Examples
:                    Some sample scripts
#Limitations
Limitations
:                 Limitations and (non-)limitations of
GNU
sed
#Other-Resources
Other Resources
:             Other resources for learning about
sed
#Reporting-Bugs
Reporting Bugs
:              Reporting bugs
#Extended-regexps
Extended regexps
:
egrep
-style regular expressions
#Concept-Index
Concept Index
:               A menu with all the topics in this manual.
#Command-and-Option-Index
Command and Option Index
:    A menu with all
sed
commands and
command-line options.
--- The detailed node listing ---
sed Programs:
#Execution-Cycle
Execution Cycle
:                  How
sed
works
#Addresses
Addresses
:                        Selecting lines with
sed
#Regular-Expressions
Regular Expressions
:              Overview of regular expression syntax
#Common-Commands
Common Commands
:                  Often used commands
#The-_0022s_0022-Command
The "s" Command
:
sed
's Swiss Army Knife
#Other-Commands
Other Commands
:                   Less frequently used commands
#Programming-Commands
Programming Commands
:             Commands for
sed
gurus
#Extended-Commands
Extended Commands
:                Commands specific of
GNU
sed
#Escapes
Escapes
:                          Specifying special characters
Examples:
#Centering-lines
Centering lines
#Increment-a-number
Increment a number
#Rename-files-to-lower-case
Rename files to lower case
#Print-bash-environment
Print bash environment
#Reverse-chars-of-lines
Reverse chars of lines
#tac
tac
:                              Reverse lines of files
#cat-_002dn
cat -n
:                           Numbering lines
#cat-_002db
cat -b
:                           Numbering non-blank lines
#wc-_002dc
wc -c
:                            Counting chars
#wc-_002dw
wc -w
:                            Counting words
#wc-_002dl
wc -l
:                            Counting lines
#head
head
:                             Printing the first lines
#tail
tail
:                             Printing the last lines
#uniq
uniq
:                             Make duplicate lines unique
#uniq-_002dd
uniq -d
:                          Print duplicated lines of input
#uniq-_002du
uniq -u
:                          Remove all duplicated lines
#cat-_002ds
cat -s
:                           Squeezing blank lines
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#Invoking-sed
Invoking sed
,
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#Top
Top
,
Up:
#Top
Top
1 Introduction
sed
is a stream editor.
A stream editor is used to perform basic text
transformations on an input stream
(a file or input from a pipeline).
While in some ways similar to an editor which
permits scripted edits (such as
ed
),
sed
works by making only one pass over the
input(s), and is consequently more efficient.
But it is
sed
's ability to filter text in a pipeline
which particularly distinguishes it from other types of
editors.
Next:
#sed-Programs
sed Programs
,
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#Introduction
Introduction
,
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#Top
Top
2 Invocation
Normally
sed
is invoked like this:
sed SCRIPT INPUTFILE...
The full format for invoking
sed
is:
sed OPTIONS... [SCRIPT] [INPUTFILE...]
If you do not specify
INPUTFILE
, or if
INPUTFILE
is
-
,
sed
filters the contents of the standard input.  The
script
is actually the first non-option parameter, which
sed
specially
considers a script and not an input file if (and only if) none of the
other
options
specifies a script to be executed, that is if neither
of the
-e
and
-f
options is specified.
sed
may be invoked with the following command-line options:
--version
Print out the version of
sed
that is being run and a copyright notice,
then exit.
--help
Print a usage message briefly summarizing these command-line options
and the bug-reporting address,
then exit.
-n
--quiet
--silent
By default,
sed
prints out the pattern space
at the end of each cycle through the script.
These options disable this automatic printing,
and
sed
only produces output when explicitly told to
via the
p
command.
-i[
SUFFIX
]
--in-place[=
SUFFIX
]
This option specifies that files are to be edited in-place.
GNU
sed
does this by creating a temporary file and
sending output to this file rather than to the standard
output.
#fn-1
1
.
This option implies
-s
.
When the end of the file is reached, the temporary file is
renamed to the output file's original name.  The extension,
if supplied, is used to modify the name of the old file
before renaming the temporary file, thereby making a backup
copy
#fn-2
2
).
This rule is followed: if the extension doesn't contain a
*
,
then it is appended to the end of the current filename as a
suffix; if the extension does contain one or more
*
characters, then
each
asterisk is replaced with the
current filename.  This allows you to add a prefix to the
backup file, instead of (or in addition to) a suffix, or
even to place backup copies of the original files into another
directory (provided the directory already exists).
If no extension is supplied, the original file is
overwritten without making a backup.
-l
N
--line-length=
N
Specify the default line-wrap length for the
l
command.
A length of 0 (zero) means to never wrap long lines.  If
not specified, it is taken to be 70.
--posix
GNU
sed
includes several extensions to
POSIX
sed.  In order to simplify writing portable scripts, this
option disables all the extensions that this manual documents,
including additional commands.
Most of the extensions accept
sed
programs that
are outside the syntax mandated by
POSIX
, but some
of them (such as the behavior of the
N
command
described in see
#Reporting-Bugs
Reporting Bugs
) actually violate the
standard.  If you want to disable only the latter kind of
extension, you can set the
POSIXLY_CORRECT
variable
to a non-empty value.
-r
--regexp-extended
Use extended regular expressions rather than basic
regular expressions.  Extended regexps are those that
egrep
accepts; they can be clearer because they
usually have less backslashes, but are a
GNU
extension
and hence scripts that use them are not portable.
See
#Extended-regexps
Extended regular expressions
.
-s
--separate
By default,
sed
will consider the files specified on the
command line as a single continuous long stream.  This
GNU
sed
extension allows the user to consider them as separate files:
range addresses (such as `
/abc/,/def/
') are not allowed
to span several files, line numbers are relative to the start
of each file,
$
refers to the last line of each file,
and files invoked from the
R
commands are rewound at the
start of each file.
-u
--unbuffered
Buffer both input and output as minimally as practical.
(This is particularly useful if the input is coming from
the likes of `
tail -f
', and you wish to see the transformed
output as soon as possible.)
-e
script
--expression=
script
Add the commands in
script
to the set of commands to be
run while processing the input.
-f
script-file
--file=
script-file
Add the commands contained in the file
script-file
to the set of commands to be run while processing the input.
If no
-e
,
-f
,
--expression
, or
--file
options are given on the command-line,
then the first non-option argument on the command line is
taken to be the
script
to be executed.
If any command-line parameters remain after processing the above,
these parameters are interpreted as the names of input files to
be processed.
A file name of `
-
' refers to the standard input stream.
The standard input will be processed if no file names are specified.
Next:
#Examples
Examples
,
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#Invoking-sed
Invoking sed
,
Up:
#Top
Top
3
sed
Programs
A
sed
program consists of one or more
sed
commands,
passed in by one or more of the
-e
,
-f
,
--expression
, and
--file
options, or the first non-option argument if zero of these
options are used.
This document will refer to “the”
sed
script;
this is understood to mean the in-order catenation
of all of the
script
s and
script-file
s passed in.
Each
sed
command consists of an optional address or
address range, followed by a one-character command name
and any additional command-specific code.
#Execution-Cycle
Execution Cycle
:           How
sed
works
#Addresses
Addresses
:                 Selecting lines with
sed
#Regular-Expressions
Regular Expressions
:       Overview of regular expression syntax
#Common-Commands
Common Commands
:           Often used commands
#The-_0022s_0022-Command
The "s" Command
:
sed
's Swiss Army Knife
#Other-Commands
Other Commands
:            Less frequently used commands
#Programming-Commands
Programming Commands
:      Commands for
sed
gurus
#Extended-Commands
Extended Commands
:         Commands specific of
GNU
sed
#Escapes
Escapes
:                   Specifying special characters
Next:
#Addresses
Addresses
,
Up:
#sed-Programs
sed Programs
3.1 How
sed
Works
sed
maintains two data buffers: the active
pattern
space,
and the auxiliary
hold
space. Both are initially empty.
sed
operates by performing the following cycle on each
lines of input: first,
sed
reads one line from the input
stream, removes any trailing newline, and places it in the pattern space.
Then commands are executed; each command can have an address associated
to it: addresses are a kind of condition code, and a command is only
executed if the condition is verified before the command is to be
executed.
When the end of the script is reached, unless the
-n
option
is in use, the contents of pattern space are printed out to the output
stream, adding back the trailing newline if it was removed.
#fn-3
3
Then the next cycle starts for the next
input line.
Unless special commands (like `
D
') are used, the pattern space is
deleted between two cycles. The hold space, on the other hand, keeps
its data between cycles (see commands `
h
', `
H
', `
x
',
`
g
', `
G
' to move data between both buffers).
Next:
#Regular-Expressions
Regular Expressions
,
Previous:
#Execution-Cycle
Execution Cycle
,
Up:
#sed-Programs
sed Programs
3.2 Selecting lines with
sed
Addresses in a
sed
script can be in any of the following forms:
number
Specifying a line number will match only that line in the input.
(Note that
sed
counts lines continuously across all input files
unless
-i
or
-s
options are specified.)
first
~
step
This
GNU
extension matches every
step
th line
starting with line
first
.
In particular, lines will be selected when there exists
a non-negative
n
such that the current line-number equals
first
+ (
n
*
step
).
Thus, to select the odd-numbered lines,
one would use
1~2
;
to pick every third line starting with the second, `
2~3
' would be used;
to pick every fifth line starting with the tenth, use `
10~5
';
and `
50~0
' is just an obscure way of saying
50
.
$
This address matches the last line of the last file of input, or
the last line of each file when the
-i
or
-s
options
are specified.
/
regexp
/
This will select any line which matches the regular expression
regexp
.
If
regexp
itself includes any
/
characters,
each must be escaped by a backslash (
\
).
The empty regular expression `
//
' repeats the last regular
expression match (the same holds if the empty regular expression is
passed to the
s
command).  Note that modifiers to regular expressions
are evaluated when the regular expression is compiled, thus it is invalid to
specify them together with the empty regular expression.
\%
regexp
%
(The
%
may be replaced by any other single character.)
This also matches the regular expression
regexp
,
but allows one to use a different delimiter than
/
.
This is particularly useful if the
regexp
itself contains
a lot of slashes, since it avoids the tedious escaping of every
/
.
If
regexp
itself includes any delimiter characters,
each must be escaped by a backslash (
\
).
/
regexp
/I
\%
regexp
%I
The
I
modifier to regular-expression matching is a
GNU
extension which causes the
regexp
to be matched in
a case-insensitive manner.
/
regexp
/M
\%
regexp
%M
The
M
modifier to regular-expression matching is a
GNU
sed
extension which causes
^
and
$
to match respectively
(in addition to the normal behavior) the empty string after a newline,
and the empty string before a newline.  There are special character
sequences
(
\`
and
\'
)
which always match the beginning or the end of the buffer.
M
stands for
multi-line
.
If no addresses are given, then all lines are matched;
if one address is given, then only lines matching that
address are matched.
An address range can be specified by specifying two addresses
separated by a comma (
,
).  An address range matches lines
starting from where the first address matches, and continues
until the second address matches (inclusively).
If the second address is a
regexp
, then checking for the
ending match will start with the line
following
the
line which matched the first address: a range will always
span at least two lines (except of course if the input stream
ends).
If the second address is a
number
less than (or equal to)
the line matching the first address, then only the one line is
matched.
GNU
sed
also supports some special two-address forms; all these
are
GNU
extensions:
0,/
regexp
/
A line number of
0
can be used in an address specification like
0,/
regexp
/
so that
sed
will try to match
regexp
in the first input line too.  In other words,
0,/
regexp
/
is similar to
1,/
regexp
/
,
except that if
addr2
matches the very first line of input the
0,/
regexp
/
form will consider it to end the range, whereas
the
1,/
regexp
/
form will match the beginning of its range and
hence make the range span up to the
second
occurrence of the
regular expression.
Note that this is the only place where the
0
address makes
sense; there is no 0-th line and commands which are given the
0
address in any other way will give an error.
addr1
,+
N
Matches
addr1
and the
N
lines following
addr1
.
addr1
,~
N
Matches
addr1
and the lines following
addr1
until the next line whose input line number is a multiple of
N
.
Appending the
!
character to the end of an address
specification negates the sense of the match.
That is, if the
!
character follows an address range,
then only lines which do
not
match the address range
will be selected.
This also works for singleton addresses,
and, perhaps perversely, for the null address.
Next:
#Common-Commands
Common Commands
,
Previous:
#Addresses
Addresses
,
Up:
#sed-Programs
sed Programs
3.3 Overview of Regular Expression Syntax
To know how to use
sed
, people should understand regular
expressions (
regexp
for short).  A regular expression
is a pattern that is matched against a
subject string from left to right.  Most characters are
ordinary
: they stand for
themselves in a pattern, and match the corresponding characters
in the subject.  As a trivial example, the pattern
The quick brown fox
matches a portion of a subject string that is identical to
itself.  The power of regular expressions comes from the
ability to include alternatives and repetitions in the pattern.
These are encoded in the pattern by the use of
special characters
,
which do not stand for themselves but instead
are interpreted in some special way.  Here is a brief description
of regular expression syntax as used in
sed
.
char
A single ordinary character matches itself.
*
Matches a sequence of zero or more instances of matches for the
preceding regular expression, which must be an ordinary character, a
special character preceded by
\
, a
.
, a grouped regexp
(see below), or a bracket expression.  As a
GNU
extension, a
postfixed regular expression can also be followed by
*
; for
example,
a**
is equivalent to
a*
.
POSIX
1003.1-2001 says that
*
stands for itself when it appears at
the start of a regular expression or subexpression, but many
non
GNU
implementations do not support this and portable
scripts should instead use
\*
in these contexts.
\+
As
*
, but matches one or more.  It is a
GNU
extension.
\?
As
*
, but only matches zero or one.  It is a
GNU
extension.
\{
i
\}
As
*
, but matches exactly
i
sequences (
i
is a
decimal integer; for portability, keep it between 0 and 255
inclusive).
\{
i
,
j
\}
Matches between
i
and
j
, inclusive, sequences.
\{
i
,\}
Matches more than or equal to
i
sequences.
\(
regexp
\)
Groups the inner
regexp
as a whole, this is used to:
Apply postfix operators, like
\(abcd\)*
:
this will search for zero or more whole sequences
of `
abcd
', while
abcd*
would search
for `
abc
' followed by zero or more occurrences
of `
d
'.  Note that support for
\(abcd\)*
is
required by
POSIX
1003.1-2001, but many non-
GNU
implementations do not support it and hence it is not universally
portable.
Use back references (see below).
.
Matches any character, including newline.
^
Matches the null string at beginning of line, i.e. what
appears after the circumflex must appear at the
beginning of line.
^#include
will match only
lines where `
#include
' is the first thing on line—if
there are spaces before, for example, the match fails.
^
acts as a special character only at the beginning
of the regular expression or subexpression (that is,
after
\(
or
\|
).  Portable scripts should avoid
^
at the beginning of a subexpression, though, as
POSIX
allows implementations that treat
^
as
an ordinary character in that context.
$
It is the same as
^
, but refers to end of line.
$
also acts as a special character only at the end
of the regular expression or subexpression (that is, before
\)
or
\|
), and its use at the end of a subexpression is not
portable.
[
list
]
[^
list
]
Matches any single character in
list
: for example,
[aeiou]
matches all vowels.  A list may include
sequences like
char1
-
char2
, which
matches any character between (inclusive)
char1
and
char2
.
A leading
^
reverses the meaning of
list
, so that
it matches any single character
not
in
list
.  To include
]
in the list, make it the first character (after
the
^
if needed), to include
-
in the list,
make it the first or last; to include
^
put
it after the first character.
The characters
$
,
*
,
.
,
[
, and
\
are normally not special within
list
.  For example,
[\*]
matches either `
\
' or `
*
', because the
\
is not
special here.  However, strings like
[.ch.]
,
[=a=]
, and
[:space:]
are special within
list
and represent collating
symbols, equivalence classes, and character classes, respectively, and
[
is therefore special within
list
when it is followed by
.
,
=
, or
:
.  Also, when not in
POSIXLY_CORRECT
mode, special escapes like
\n
and
\t
are recognized within
list
.  See
#Escapes
Escapes
.
regexp1
\|
regexp2
Matches either
regexp1
or
regexp2
.  Use
parentheses to use complex alternative regular expressions.
The matching process tries each alternative in turn, from
left to right, and the first one that succeeds is used.
It is a
GNU
extension.
regexp1
regexp2
Matches the concatenation of
regexp1
and
regexp2
.
Concatenation binds more tightly than
\|
,
^
, and
$
, but less tightly than the other regular expression
operators.
\
digit
Matches the
digit
-th
\(...\)
parenthesized
subexpression in the regular expression.  This is called a
back
reference
.  Subexpressions are implicity numbered by counting
occurrences of
\(
left-to-right.
\n
Matches the newline character.
\
char
Matches
char
, where
char
is one of
$
,
*
,
.
,
[
,
\
, or
^
.
Note that the only C-like
backslash sequences that you can portably assume to be
interpreted are
\n
and
\\
; in particular
\t
is not portable, and matches a `
t
' under most
implementations of
sed
, rather than a tab character.
Note that the regular expression matcher is greedy, i.e., matches
are attempted from left to right and, if two or more matches are
possible starting at the same character, it selects the longest.
Examples:
`
abcdef
'
Matches `
abcdef
'.
`
a*b
'
Matches zero or more `
a
's followed by a single
`
b
'.  For example, `
b
' or `
aaaaab
'.
`
a\?b
'
Matches `
b
' or `
ab
'.
`
a\+b\+
'
Matches one or more `
a
's followed by one or more
`
b
's: `
ab
' is the shortest possible match, but
other examples are `
aaaab
' or `
abbbbb
' or
`
aaaaaabbbbbbb
'.
`
.*
'
`
.\+
'
These two both match all the characters in a string;
however, the first matches every string (including the empty
string), while the second matches only strings containing
at least one character.
`
^main.*(.*)
'
his matches a string starting with `
main
',
followed by an opening and closing
parenthesis.  The `
n
', `
(
' and `
)
' need not
be adjacent.
`
^#
'
This matches a string beginning with `
#
'.
`
\\$
'
This matches a string ending with a single backslash.  The
regexp contains two backslashes for escaping.
`
\$
'
Instead, this matches a string consisting of a single dollar sign,
because it is escaped.
`
[a-zA-Z0-9]
'
In the C locale, this matches any
ASCII
letters or digits.
`
[^
tab
]\+
'
(Here
tab
stands for a single tab character.)
This matches a string of one or more
characters, none of which is a space or a tab.
Usually this means a word.
`
^\(.*\)\n\1$
'
This matches a string consisting of two equal substrings separated by
a newline.
`
.\{9\}A$
'
This matches nine characters followed by an `
A
'.
`
^.\{15\}A
'
This matches the start of a string that contains 16 characters,
the last of which is an `
A
'.
Next:
#The-_0022s_0022-Command
The "s" Command
,
Previous:
#Regular-Expressions
Regular Expressions
,
Up:
#sed-Programs
sed Programs
3.4 Often-Used Commands
If you use
sed
at all, you will quite likely want to know
these commands.
#
[No addresses allowed.]
The
#
character begins a comment;
the comment continues until the next newline.
If you are concerned about portability, be aware that
some implementations of
sed
(which are not
posix
conformant) may only support a single one-line comment,
and then only when the very first character of the script is a
#
.
Warning: if the first two characters of the
sed
script
are
#n
, then the
-n
(no-autoprint) option is forced.
If you want to put a comment in the first line of your script
and that comment begins with the letter `
n
'
and you do not want this behavior,
then be sure to either use a capital `
N
',
or place at least one space before the `
n
'.
q [
exit-code
]
This command only accepts a single address.
Exit
sed
without processing any more commands or input.
Note that the current pattern space is printed if auto-print is
not disabled with the
-n
options.  The ability to return
an exit code from the
sed
script is a
GNU
sed
extension.
d
Delete the pattern space;
immediately start next cycle.
p
Print out the pattern space (to the standard output).
This command is usually only used in conjunction with the
-n
command-line option.
n
If auto-print is not disabled, print the pattern space,
then, regardless, replace the pattern space with the next line of input.
If there is no more input then
sed
exits without processing
any more commands.
{
commands
}
A group of commands may be enclosed between
{
and
}
characters.
This is particularly useful when you want a group of commands
to be triggered by a single address (or address-range) match.
Next:
#Other-Commands
Other Commands
,
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#Common-Commands
Common Commands
,
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#sed-Programs
sed Programs
3.5 The
s
Command
The syntax of the
s
(as in substitute) command is
`
s/
regexp
/
replacement
/
flags
'.  The
/
characters may be uniformly replaced by any other single
character within any given
s
command.  The
/
character (or whatever other character is used in its stead)
can appear in the
regexp
or
replacement
only if it is preceded by a
\
character.
The
s
command is probably the most important in
sed
and has a lot of different options.  Its basic concept is simple:
the
s
command attempts to match the pattern
space against the supplied
regexp
; if the match is
successful, then that portion of the pattern
space which was matched is replaced with
replacement
.
The
replacement
can contain
\
n
(
n
being
a number from 1 to 9, inclusive) references, which refer to
the portion of the match which is contained between the
n
th
\(
and its matching
\)
.
Also, the
replacement
can contain unescaped
&
characters which reference the whole matched portion
of the pattern space.
Finally, as a
GNU
sed
extension, you can include a
special sequence made of a backslash and one of the letters
L
,
l
,
U
,
u
, or
E
.
The meaning is as follows:
\L
Turn the replacement
to lowercase until a
\U
or
\E
is found,
\l
Turn the
next character to lowercase,
\U
Turn the replacement to uppercase
until a
\L
or
\E
is found,
\u
Turn the next character
to uppercase,
\E
Stop case conversion started by
\L
or
\U
.
To include a literal
\
,
&
, or newline in the final
replacement, be sure to precede the desired
\
,
&
,
or newline in the
replacement
with a
\
.
The
s
command can be followed by zero or more of the
following
flags
:
g
Apply the replacement to
all
matches to the
regexp
,
not just the first.
number
Only replace the
number
th match of the
regexp
.
Note: the
posix
standard does not specify what should happen
when you mix the
g
and
number
modifiers,
and currently there is no widely agreed upon meaning
across
sed
implementations.
For
GNU
sed
, the interaction is defined to be:
ignore matches before the
number
th,
and then match and replace all matches from
the
number
th on.
p
If the substitution was made, then print the new pattern space.
Note: when both the
p
and
e
options are specified,
the relative ordering of the two produces very different results.
In general,
ep
(evaluate then print) is what you want,
but operating the other way round can be useful for debugging.
For this reason, the current version of
GNU
sed
interprets
specially the presence of
p
options both before and after
e
, printing the pattern space before and after evaluation,
while in general flags for the
s
command show their
effect just once.  This behavior, although documented, might
change in future versions.
w
file-name
If the substitution was made, then write out the result to the named file.
As a
GNU
sed
extension, two special values of
file-name
are
supported:
/dev/stderr
, which writes the result to the standard
error, and
/dev/stdout
, which writes to the standard
output.
#fn-4
4
e
This command allows one to pipe input from a shell command
into pattern space.  If a substitution was made, the command
that is found in pattern space is executed and pattern space
is replaced with its output.  A trailing newline is suppressed;
results are undefined if the command to be executed contains
a
nul
character.  This is a
GNU
sed
extension.
I
i
The
I
modifier to regular-expression matching is a
GNU
extension which makes
sed
match
regexp
in a
case-insensitive manner.
M
m
The
M
modifier to regular-expression matching is a
GNU
sed
extension which causes
^
and
$
to match respectively
(in addition to the normal behavior) the empty string after a newline,
and the empty string before a newline.  There are special character
sequences
(
\`
and
\'
)
which always match the beginning or the end of the buffer.
M
stands for
multi-line
.
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#Programming-Commands
Programming Commands
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#The-_0022s_0022-Command
The "s" Command
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Up:
#sed-Programs
sed Programs
3.6 Less Frequently-Used Commands
Though perhaps less frequently used than those in the previous
section, some very small yet useful
sed
scripts can be built with
these commands.
y/
source-chars
/
dest-chars
/
(The
/
characters may be uniformly replaced by
any other single character within any given
y
command.)
Transliterate any characters in the pattern space which match
any of the
source-chars
with the corresponding character
in
dest-chars
.
Instances of the
/
(or whatever other character is used in its stead),
\
, or newlines can appear in the
source-chars
or
dest-chars
lists, provide that each instance is escaped by a
\
.
The
source-chars
and
dest-chars
lists
must
contain the same number of characters (after de-escaping).
a\
text
As a
GNU
extension, this command accepts two addresses.
Queue the lines of text which follow this command
(each but the last ending with a
\
,
which are removed from the output)
to be output at the end of the current cycle,
or when the next input line is read.
Escape sequences in
text
are processed, so you should
use
\\
in
text
to print a single backslash.
As a
GNU
extension, if between the
a
and the newline there is
other than a whitespace-
\
sequence, then the text of this line,
starting at the first non-whitespace character after the
a
,
is taken as the first line of the
text
block.
(This enables a simplification in scripting a one-line add.)
This extension also works with the
i
and
c
commands.
i\
text
As a
GNU
extension, this command accepts two addresses.
Immediately output the lines of text which follow this command
(each but the last ending with a
\
,
which are removed from the output).
c\
text
Delete the lines matching the address or address-range,
and output the lines of text which follow this command
(each but the last ending with a
\
,
which are removed from the output)
in place of the last line
(or in place of each line, if no addresses were specified).
A new cycle is started after this command is done,
since the pattern space will have been deleted.
=
As a
GNU
extension, this command accepts two addresses.
Print out the current input line number (with a trailing newline).
l
n
Print the pattern space in an unambiguous form:
non-printable characters (and the
\
character)
are printed in C-style escaped form; long lines are split,
with a trailing
\
character to indicate the split;
the end of each line is marked with a
$
.
n
specifies the desired line-wrap length;
a length of 0 (zero) means to never wrap long lines.  If omitted,
the default as specified on the command line is used.  The
n
parameter is a
GNU
sed
extension.
r
filename
As a
GNU
extension, this command accepts two addresses.
Queue the contents of
filename
to be read and
inserted into the output stream at the end of the current cycle,
or when the next input line is read.
Note that if
filename
cannot be read, it is treated as
if it were an empty file, without any error indication.
As a
GNU
sed
extension, the special value
/dev/stdin
is supported for the file name, which reads the contents of the
standard input.
w
filename
Write the pattern space to
filename
.
As a
GNU
sed
extension, two special values of
file-name
are
supported:
/dev/stderr
, which writes the result to the standard
error, and
/dev/stdout
, which writes to the standard
output.
#fn-5
5
The file will be created (or truncated) before the
first input line is read; all
w
commands
(including instances of
w
flag on successful
s
commands)
which refer to the same
filename
are output without
closing and reopening the file.
D
Delete text in the pattern space up to the first newline.
If any text is left, restart cycle with the resultant
pattern space (without reading a new line of input),
otherwise start a normal new cycle.
N
Add a newline to the pattern space,
then append the next line of input to the pattern space.
If there is no more input then
sed
exits without processing
any more commands.
P
Print out the portion of the pattern space up to the first newline.
h
Replace the contents of the hold space with the contents of the pattern space.
H
Append a newline to the contents of the hold space,
and then append the contents of the pattern space to that of the hold space.
g
Replace the contents of the pattern space with the contents of the hold space.
G
Append a newline to the contents of the pattern space,
and then append the contents of the hold space to that of the pattern space.
x
Exchange the contents of the hold and pattern spaces.
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#Extended-Commands
Extended Commands
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#Other-Commands
Other Commands
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#sed-Programs
sed Programs
3.7 Commands for
sed
gurus
In most cases, use of these commands indicates that you are
probably better off programming in something like
awk
or Perl.  But occasionally one is committed to sticking
with
sed
, and these commands can enable one to write
quite convoluted scripts.
:
label
[No addresses allowed.]
Specify the location of
label
for branch commands.
In all other respects, a no-op.
b
label
Unconditionally branch to
label
.
The
label
may be omitted, in which case the next cycle is started.
t
label
Branch to
label
only if there has been a successful
s
ubstitution
since the last input line was read or conditional branch was taken.
The
label
may be omitted, in which case the next cycle is started.
Next:
#Escapes
Escapes
,
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#Programming-Commands
Programming Commands
,
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#sed-Programs
sed Programs
3.8 Commands Specific to
GNU
sed
These commands are specific to
GNU
sed
, so you
must use them with care and only when you are sure that
hindering portability is not evil.  They allow you to check
for
GNU
sed
extensions or to do tasks that are required
quite often, yet are unsupported by standard
sed
s.
e [
command
]
This command allows one to pipe input from a shell command
into pattern space.  Without parameters, the
e
command
executes the command that is found in pattern space and
replaces the pattern space with the output; a trailing newline
is suppressed.
If a parameter is specified, instead, the
e
command
interprets it as a command and sends its output to the output stream
(like
r
does).  The command can run across multiple
lines, all but the last ending with a back-slash.
In both cases, the results are undefined if the command to be
executed contains a
nul
character.
L
n
This
GNU
sed
extension fills and joins lines in pattern space
to produce output lines of (at most)
n
characters, like
fmt
does; if
n
is omitted, the default as specified
on the command line is used.  This command is considered a failed
experiment and unless there is enough request (which seems unlikely)
will be removed in future versions.
Q [
exit-code
]
This command only accepts a single address.
This command is the same as
q
, but will not print the
contents of pattern space.  Like
q
, it provides the
ability to return an exit code to the caller.
This command can be useful because the only alternative ways
to accomplish this apparently trivial function are to use
the
-n
option (which can unnecessarily complicate
your script) or resorting to the following snippet, which
wastes time by reading the whole file without any visible effect:
:eat
$d
Quit silently on the last line
N
Read another line, silently
g
Overwrite pattern space each time to save memory
b eat
R
filename
Queue a line of
filename
to be read and
inserted into the output stream at the end of the current cycle,
or when the next input line is read.
Note that if
filename
cannot be read, or if its end is
reached, no line is appended, without any error indication.
As with the
r
command, the special value
/dev/stdin
is supported for the file name, which reads a line from the
standard input.
T
label
Branch to
label
only if there have been no successful
s
ubstitutions since the last input line was read or
conditional branch was taken. The
label
may be omitted,
in which case the next cycle is started.
v
version
This command does nothing, but makes
sed
fail if
GNU
sed
extensions are not supported, simply because other
versions of
sed
do not implement it.  In addition, you
can specify the version of
sed
that your script
requires, such as
4.0.5
.  The default is
4.0
because that is the first version that implemented this command.
This command enables all
GNU
extensions even if
POSIXLY_CORRECT
is set in the environment.
W
filename
Write to the given filename the portion of the pattern space up to
the first newline.  Everything said under the
w
command about
file handling holds here too.
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#Extended-Commands
Extended Commands
,
Up:
#sed-Programs
sed Programs
3.9
GNU
Extensions for Escapes in Regular Expressions
Until this chapter, we have only encountered escapes of the form
`
\^
', which tell
sed
not to interpret the circumflex
as a special character, but rather to take it literally.  For
example, `
\*
' matches a single asterisk rather than zero
or more backslashes.
This chapter introduces another kind of escape
#fn-6
6
—that
is, escapes that are applied to a character or sequence of characters
that ordinarily are taken literally, and that
sed
replaces
with a special character.  This provides a way
of encoding non-printable characters in patterns in a visible manner.
There is no restriction on the appearance of non-printing characters
in a
sed
script but when a script is being prepared in the
shell or by text editing, it is usually easier to use one of
the following escape sequences than the binary character it
represents:
The list of these escapes is:
\a
Produces or matches a
bel
character, that is an “alert” (
ascii
7).
\f
Produces or matches a form feed (
ascii
12).
\n
Produces or matches a newline (
ascii
10).
\r
Produces or matches a carriage return (
ascii
13).
\t
Produces or matches a horizontal tab (
ascii
9).
\v
Produces or matches a so called “vertical tab” (
ascii
11).
\c
x
Produces or matches
Control
-
x
, where
x
is
any character.  The precise effect of `
\c
x
' is as follows:
if
x
is a lower case letter, it is converted to upper case.
Then bit 6 of the character (hex 40) is inverted.  Thus `
\cz
' becomes
hex 1A, but `
\c{
' becomes hex 3B, while `
\c;
' becomes hex 7B.
\d
xxx
Produces or matches a character whose decimal
ascii
value is
xxx
.
\o
xxx
Produces or matches a character whose octal
ascii
value is
xxx
.
\x
xx
Produces or matches a character whose hexadecimal
ascii
value is
xx
.
`
\b
' (backspace) was omitted because of the conflict with
the existing “word boundary” meaning.
Other escapes match a particular character class and are valid only in
regular expressions:
\w
Matches any “word” character.  A “word” character is any
letter or digit or the underscore character.
\W
Matches any “non-word” character.
\b
Matches a word boundary; that is it matches if the character
to the left is a “word” character and the character to the
right is a “non-word” character, or vice-versa.
\B
Matches everywhere but on a word boundary; that is it matches
if the character to the left and the character to the right
are either both “word” characters or both “non-word”
characters.
\`
Matches only at the start of pattern space.  This is different
from
^
in multi-line mode.
\'
Matches only at the end of pattern space.  This is different
from
$
in multi-line mode.
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#Limitations
Limitations
,
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#sed-Programs
sed Programs
,
Up:
#Top
Top
4 Some Sample Scripts
Here are some
sed
scripts to guide you in the art of mastering
sed
.
Some exotic examples:
#Centering-lines
Centering lines
#Increment-a-number
Increment a number
#Rename-files-to-lower-case
Rename files to lower case
#Print-bash-environment
Print bash environment
#Reverse-chars-of-lines
Reverse chars of lines
Emulating standard utilities:
#tac
tac
:                              Reverse lines of files
#cat-_002dn
cat -n
:                           Numbering lines
#cat-_002db
cat -b
:                           Numbering non-blank lines
#wc-_002dc
wc -c
:                            Counting chars
#wc-_002dw
wc -w
:                            Counting words
#wc-_002dl
wc -l
:                            Counting lines
#head
head
:                             Printing the first lines
#tail
tail
:                             Printing the last lines
#uniq
uniq
:                             Make duplicate lines unique
#uniq-_002dd
uniq -d
:                          Print duplicated lines of input
#uniq-_002du
uniq -u
:                          Remove all duplicated lines
#cat-_002ds
cat -s
:                           Squeezing blank lines
Next:
#Increment-a-number
Increment a number
,
Up:
#Examples
Examples
4.1 Centering Lines
This script centers all lines of a file on a 80 columns width.
To change that width, the number in
\{...\}
must be
replaced, and the number of added spaces also must be changed.
Note how the buffer commands are used to separate parts in
the regular expressions to be matched—this is a common
technique.
#!/usr/bin/sed -f
# Put 80 spaces in the buffer
1 {
x
s/^$/          /
s/^.*$/&&&&&&&&/
x
}
# del leading and trailing spaces
y/
tab
/ /
s/^ *//
s/ *$//
# add a newline and 80 spaces to end of line
G
# keep first 81 chars (80 + a newline)
s/^\(.\{81\}\).*$/\1/
# \2 matches half of the spaces, which are moved to the beginning
s/^\(.*\)\n\(.*\)\2/\2\1/
Next:
#Rename-files-to-lower-case
Rename files to lower case
,
Previous:
#Centering-lines
Centering lines
,
Up:
#Examples
Examples
4.2 Increment a Number
This script is one of a few that demonstrate how to do arithmetic
in
sed
.  This is indeed possible,
#fn-7
7
but must be done manually.
To increment one number you just add 1 to last digit, replacing
it by the following digit.  There is one exception: when the digit
is a nine the previous digits must be also incremented until you
don't have a nine.
This solution by Bruno Haible is very clever and smart because
it uses a single buffer; if you don't have this limitation, the
algorithm used in
#cat-_002dn
Numbering lines
, is faster.
It works by replacing trailing nines with an underscore, then
using multiple
s
commands to increment the last digit,
and then again substituting underscores with zeros.
#!/usr/bin/sed -f
/[^0-9]/ d
# replace all leading 9s by _ (any other character except digits, could
# be used)
:d
s/9\(_*\)$/_\1/
td
# incr last digit only.  The first line adds a most-significant
# digit of 1 if we have to add a digit.
#
# The
tn
commands are not necessary, but make the thing
# faster
s/^\(_*\)$/1\1/; tn
s/8\(_*\)$/9\1/; tn
s/7\(_*\)$/8\1/; tn
s/6\(_*\)$/7\1/; tn
s/5\(_*\)$/6\1/; tn
s/4\(_*\)$/5\1/; tn
s/3\(_*\)$/4\1/; tn
s/2\(_*\)$/3\1/; tn
s/1\(_*\)$/2\1/; tn
s/0\(_*\)$/1\1/; tn
:n
y/_/0/
Next:
#Print-bash-environment
Print bash environment
,
Previous:
#Increment-a-number
Increment a number
,
Up:
#Examples
Examples
4.3 Rename Files to Lower Case
This is a pretty strange use of
sed
.  We transform text, and
transform it to be shell commands, then just feed them to shell.
Don't worry, even worse hacks are done when using
sed
; I have
seen a script converting the output of
date
into a
bc
program!
The main body of this is the
sed
script, which remaps the name
from lower to upper (or vice-versa) and even checks out
if the remapped name is the same as the original name.
Note how the script is parameterized using shell
variables and proper quoting.
#! /bin/sh
# rename files to lower/upper case...
#
# usage:
#    move-to-lower *
#    move-to-upper *
# or
#    move-to-lower -R .
#    move-to-upper -R .
#
help()
{
cat << eof
Usage: $0 [-n] [-r] [-h] files...
-n      do nothing, only see what would be done
-R      recursive (use find)
-h      this message
files   files to remap to lower case
Examples:
$0 -n *        (see if everything is ok, then...)
$0 *
$0 -R .
eof
}
apply_cmd='sh'
finder='echo "$@" | tr " " "\n"'
files_only=
while :
do
case "$1" in
-n) apply_cmd='cat' ;;
-R) finder='find "$@" -type f';;
-h) help ; exit 1 ;;
*) break ;;
esac
shift
done
if [ -z "$1" ]; then
echo Usage: $0 [-h] [-n] [-r] files...
exit 1
fi
LOWER='abcdefghijklmnopqrstuvwxyz'
UPPER='ABCDEFGHIJKLMNOPQRSTUVWXYZ'
case `basename $0` in
*upper*) TO=$UPPER; FROM=$LOWER ;;
*)       FROM=$UPPER; TO=$LOWER ;;
esac
eval $finder | sed -n '
# remove all trailing slashes
s/\/*$//
# add ./ if there is no path, only a filename
/\//! s/^/.\//
# save path+filename
h
# remove path
s/.*\///
# do conversion only on filename
y/'$FROM'/'$TO'/
# now line contains original path+file, while
# hold space contains the new filename
x
# add converted file name to line, which now contains
# path/file-name\nconverted-file-name
G
# check if converted file name is equal to original file name,
# if it is, do not print nothing
/^.*\/\(.*\)\n\1/b
# now, transform path/fromfile\n, into
# mv path/fromfile path/tofile and print it
s/^\(.*\/\)\(.*\)\n\(.*\)$/mv \1\2 \1\3/p
' | $apply_cmd
Next:
#Reverse-chars-of-lines
Reverse chars of lines
,
Previous:
#Rename-files-to-lower-case
Rename files to lower case
,
Up:
#Examples
Examples
4.4 Print
bash
Environment
This script strips the definition of the shell functions
from the output of the
set
Bourne-shell command.
#!/bin/sh
set | sed -n '
:x
# if no occurrence of `
=()
' print and load next line
/=()/! { p; b; }
/ () $/! { p; b; }
# possible start of functions section
# save the line in case this is a var like FOO="() "
h
# if the next line has a brace, we quit because
# nothing comes after functions
n
/^{/ q
# print the old line
x; p
# work on the new line now
x; bx
'
Next:
#tac
tac
,
Previous:
#Print-bash-environment
Print bash environment
,
Up:
#Examples
Examples
4.5 Reverse Characters of Lines
This script can be used to reverse the position of characters
in lines.  The technique moves two characters at a time, hence
it is faster than more intuitive implementations.
Note the
tx
command before the definition of the label.
This is often needed to reset the flag that is tested by
the
t
command.
Imaginative readers will find uses for this script.  An example
is reversing the output of
banner
.
#fn-8
8
#!/usr/bin/sed -f
/../! b
# Reverse a line.  Begin embedding the line between two newlines
s/^.*$/\
&\
/
# Move first character at the end.  The regexp matches until
# there are zero or one characters between the markers
tx
:x
s/\(\n.\)\(.*\)\(.\n\)/\3\2\1/
tx
# Remove the newline markers
s/\n//g
Next:
#cat-_002dn
cat -n
,
Previous:
#Reverse-chars-of-lines
Reverse chars of lines
,
Up:
#Examples
Examples
4.6 Reverse Lines of Files
This one begins a series of totally useless (yet interesting)
scripts emulating various Unix commands.  This, in particular,
is a
tac
workalike.
Note that on implementations other than
GNU
sed
this script might easily overflow internal buffers.
#!/usr/bin/sed -nf
# reverse all lines of input, i.e. first line became last, ...
# from the second line, the buffer (which contains all previous lines)
# is *appended* to current line, so, the order will be reversed
1! G
# on the last line we're done -- print everything
$ p
# store everything on the buffer again
h
Next:
#cat-_002db
cat -b
,
Previous:
#tac
tac
,
Up:
#Examples
Examples
4.7 Numbering Lines
This script replaces `
cat -n
'; in fact it formats its output
exactly like
GNU
cat
does.
Of course this is completely useless and for two reasons:  first,
because somebody else did it in C, second, because the following
Bourne-shell script could be used for the same purpose and would
be much faster:
#! /bin/sh
sed -e "=" $@ | sed -e '
s/^/      /
N
s/^ *\(......\)\n/\1  /
'
It uses
sed
to print the line number, then groups lines two
by two using
N
.  Of course, this script does not teach as much as
the one presented below.
The algorithm used for incrementing uses both buffers, so the line
is printed as soon as possible and then discarded.  The number
is split so that changing digits go in a buffer and unchanged ones go
in the other; the changed digits are modified in a single step
(using a
y
command).  The line number for the next line
is then composed and stored in the hold space, to be used in the
next iteration.
#!/usr/bin/sed -nf
# Prime the pump on the first line
x
/^$/ s/^.*$/1/
# Add the correct line number before the pattern
G
h
# Format it and print it
s/^/      /
s/^ *\(......\)\n/\1  /p
# Get the line number from hold space; add a zero
# if we're going to add a digit on the next line
g
s/\n.*$//
/^9*$/ s/^/0/
# separate changing/unchanged digits with an x
s/.9*$/x&/
# keep changing digits in hold space
h
s/^.*x//
y/0123456789/1234567890/
x
# keep unchanged digits in pattern space
s/x.*$//
# compose the new number, remove the newline implicitly added by G
G
s/\n//
h
Next:
#wc-_002dc
wc -c
,
Previous:
#cat-_002dn
cat -n
,
Up:
#Examples
Examples
4.8 Numbering Non-blank Lines
Emulating `
cat -b
' is almost the same as `
cat -n
'—we only
have to select which lines are to be numbered and which are not.
The part that is common to this script and the previous one is
not commented to show how important it is to comment
sed
scripts properly...
#!/usr/bin/sed -nf
/^$/ {
p
b
}
# Same as cat -n from now
x
/^$/ s/^.*$/1/
G
h
s/^/      /
s/^ *\(......\)\n/\1  /p
x
s/\n.*$//
/^9*$/ s/^/0/
s/.9*$/x&/
h
s/^.*x//
y/0123456789/1234567890/
x
s/x.*$//
G
s/\n//
h
Next:
#wc-_002dw
wc -w
,
Previous:
#cat-_002db
cat -b
,
Up:
#Examples
Examples
4.9 Counting Characters
This script shows another way to do arithmetic with
sed
.
In this case we have to add possibly large numbers, so implementing
this by successive increments would not be feasible (and possibly
even more complicated to contrive than this script).
The approach is to map numbers to letters, kind of an abacus
implemented with
sed
.  `
a
's are units, `
b
's are
tenths and so on: we simply add the number of characters
on the current line as units, and then propagate the carry
to tenths, hundredths, and so on.
As usual, running totals are kept in hold space.
On the last line, we convert the abacus form back to decimal.
For the sake of variety, this is done with a loop rather than
with some 80
s
commands
#fn-9
9
: first we
convert units, removing `
a
's from the number; then we
rotate letters so that tenths become `
a
's, and so on
until no more letters remain.
#!/usr/bin/sed -nf
# Add n+1 a's to hold space (+1 is for the newline)
s/./a/g
H
x
s/\n/a/
# Do the carry.  The t's and b's are not necessary,
# but they do speed up the thing
t a
: a;  s/aaaaaaaaaa/b/g; t b; b done
: b;  s/bbbbbbbbbb/c/g; t c; b done
: c;  s/cccccccccc/d/g; t d; b done
: d;  s/dddddddddd/e/g; t e; b done
: e;  s/eeeeeeeeee/f/g; t f; b done
: f;  s/ffffffffff/g/g; t g; b done
: g;  s/gggggggggg/h/g; t h; b done
: h;  s/hhhhhhhhhh//g
: done
$! {
h
b
}
# On the last line, convert back to decimal
: loop
/a/! s/[b-h]*/&0/
s/aaaaaaaaa/9/
s/aaaaaaaa/8/
s/aaaaaaa/7/
s/aaaaaa/6/
s/aaaaa/5/
s/aaaa/4/
s/aaa/3/
s/aa/2/
s/a/1/
: next
y/bcdefgh/abcdefg/
/[a-h]/ b loop
p
Next:
#wc-_002dl
wc -l
,
Previous:
#wc-_002dc
wc -c
,
Up:
#Examples
Examples
4.10 Counting Words
This script is almost the same as the previous one, once each
of the words on the line is converted to a single `
a
'
(in the previous script each letter was changed to an `
a
').
It is interesting that real
wc
programs have optimized
loops for `
wc -c
', so they are much slower at counting
words rather than characters.  This script's bottleneck,
instead, is arithmetic, and hence the word-counting one
is faster (it has to manage smaller numbers).
Again, the common parts are not commented to show the importance
of commenting
sed
scripts.
#!/usr/bin/sed -nf
# Convert words to a's
s/[
tab
][
tab
]*/ /g
s/^/ /
s/ [^ ][^ ]*/a /g
s/ //g
# Append them to hold space
H
x
s/\n//
# From here on it is the same as in wc -c.
/aaaaaaaaaa/! bx;   s/aaaaaaaaaa/b/g
/bbbbbbbbbb/! bx;   s/bbbbbbbbbb/c/g
/cccccccccc/! bx;   s/cccccccccc/d/g
/dddddddddd/! bx;   s/dddddddddd/e/g
/eeeeeeeeee/! bx;   s/eeeeeeeeee/f/g
/ffffffffff/! bx;   s/ffffffffff/g/g
/gggggggggg/! bx;   s/gggggggggg/h/g
s/hhhhhhhhhh//g
:x
$! { h; b; }
:y
/a/! s/[b-h]*/&0/
s/aaaaaaaaa/9/
s/aaaaaaaa/8/
s/aaaaaaa/7/
s/aaaaaa/6/
s/aaaaa/5/
s/aaaa/4/
s/aaa/3/
s/aa/2/
s/a/1/
y/bcdefgh/abcdefg/
/[a-h]/ by
p
Next:
#head
head
,
Previous:
#wc-_002dw
wc -w
,
Up:
#Examples
Examples
4.11 Counting Lines
No strange things are done now, because
sed
gives us
`
wc -l
' functionality for free!!! Look:
#!/usr/bin/sed -nf
$=
Next:
#tail
tail
,
Previous:
#wc-_002dl
wc -l
,
Up:
#Examples
Examples
4.12 Printing the First Lines
This script is probably the simplest useful
sed
script.
It displays the first 10 lines of input; the number of displayed
lines is right before the
q
command.
#!/usr/bin/sed -f
10q
Next:
#uniq
uniq
,
Previous:
#head
head
,
Up:
#Examples
Examples
4.13 Printing the Last Lines
Printing the last
n
lines rather than the first is more complex
but indeed possible.
n
is encoded in the second line, before
the bang character.
This script is similar to the
tac
script in that it keeps the
final output in the hold space and prints it at the end:
#!/usr/bin/sed -nf
1! {; H; g; }
1,10 !s/[^\n]*\n//
$p
h
Mainly, the scripts keeps a window of 10 lines and slides it
by adding a line and deleting the oldest (the substitution command
on the second line works like a
D
command but does not
restart the loop).
The “sliding window” technique is a very powerful way to write
efficient and complex
sed
scripts, because commands like
P
would require a lot of work if implemented manually.
To introduce the technique, which is fully demonstrated in the
rest of this chapter and is based on the
N
,
P
and
D
commands, here is an implementation of
tail
using a simple “sliding window.”
This looks complicated but in fact the working is the same as
the last script: after we have kicked in the appropriate number
of lines, however, we stop using the hold space to keep inter-line
state, and instead use
N
and
D
to slide pattern
space by one line:
#!/usr/bin/sed -f
1h
2,10 {; H; g; }
$q
1,9d
N
D
Next:
#uniq-_002dd
uniq -d
,
Previous:
#tail
tail
,
Up:
#Examples
Examples
4.14 Make Duplicate Lines Unique
This is an example of the art of using the
N
,
P
and
D
commands, probably the most difficult to master.
#!/usr/bin/sed -f
h
:b
# On the last line, print and exit
$b
N
/^\(.*\)\n\1$/ {
# The two lines are identical.  Undo the effect of
# the n command.
g
bb
}
# If the
N
command had added the last line, print and exit
$b
# The lines are different; print the first and go
# back working on the second.
P
D
As you can see, we mantain a 2-line window using
P
and
D
.
This technique is often used in advanced
sed
scripts.
Next:
#uniq-_002du
uniq -u
,
Previous:
#uniq
uniq
,
Up:
#Examples
Examples
4.15 Print Duplicated Lines of Input
This script prints only duplicated lines, like `
uniq -d
'.
#!/usr/bin/sed -nf
$b
N
/^\(.*\)\n\1$/ {
# Print the first of the duplicated lines
s/.*\n//
p
# Loop until we get a different line
:b
$b
N
/^\(.*\)\n\1$/ {
s/.*\n//
bb
}
}
# The last line cannot be followed by duplicates
$b
# Found a different one.  Leave it alone in the pattern space
# and go back to the top, hunting its duplicates
D
Next:
#cat-_002ds
cat -s
,
Previous:
#uniq-_002dd
uniq -d
,
Up:
#Examples
Examples
4.16 Remove All Duplicated Lines
This script prints only unique lines, like `
uniq -u
'.
#!/usr/bin/sed -f
# Search for a duplicate line --- until that, print what you find.
$b
N
/^\(.*\)\n\1$/ ! {
P
D
}
:c
# Got two equal lines in pattern space.  At the
# end of the file we simply exit
$d
# Else, we keep reading lines with
N
until we
# find a different one
s/.*\n//
N
/^\(.*\)\n\1$/ {
bc
}
# Remove the last instance of the duplicate line
# and go back to the top
D
Previous:
#uniq-_002du
uniq -u
,
Up:
#Examples
Examples
4.17 Squeezing Blank Lines
As a final example, here are three scripts, of increasing complexity
and speed, that implement the same function as `
cat -s
', that is
squeezing blank lines.
The first leaves a blank line at the beginning and end if there are
some already.
#!/usr/bin/sed -f
# on empty lines, join with next
# Note there is a star in the regexp
:x
/^\n*$/ {
N
bx
}
# now, squeeze all '\n', this can be also done by:
# s/^\(\n\)*/\1/
s/\n*/\
/
This one is a bit more complex and removes all empty lines
at the beginning.  It does leave a single blank line at end
if one was there.
#!/usr/bin/sed -f
# delete all leading empty lines
1,/^./{
/./!d
}
# on an empty line we remove it and all the following
# empty lines, but one
:x
/./!{
N
s/^\n$//
tx
}
This removes leading and trailing blank lines.  It is also the
fastest.  Note that loops are completely done with
n
and
b
, without exploting the fact that
sed
cycles back
to the top of the script automatically at the end of a line.
#!/usr/bin/sed -nf
# delete all (leading) blanks
/./!d
# get here: so there is a non empty
:x
# print it
p
# get next
n
# got chars? print it again, etc...
/./bx
# no, don't have chars: got an empty line
:z
# get next, if last line we finish here so no trailing
# empty lines are written
n
# also empty? then ignore it, and get next... this will
# remove ALL empty lines
/./!bz
# all empty lines were deleted/ignored, but we have a non empty.  As
# what we want to do is to squeeze, insert a blank line artificially
i\
bx
Next:
#Other-Resources
Other Resources
,
Previous:
#Examples
Examples
,
Up:
#Top
Top
5
GNU
sed
's Limitations and Non-limitations
For those who want to write portable
sed
scripts,
be aware that some implementations have been known to
limit line lengths (for the pattern and hold spaces)
to be no more than 4000 bytes.
The
posix
standard specifies that conforming
sed
implementations shall support at least 8192 byte line lengths.
GNU
sed
has no built-in limit on line length;
as long as it can
malloc()
more (virtual) memory,
you can feed or construct lines as long as you like.
However, recursion is used to handle subpatterns and indefinite
repetition.  This means that the available stack space may limit
the size of the buffer that can be processed by certain patterns.
Next:
#Reporting-Bugs
Reporting Bugs
,
Previous:
#Limitations
Limitations
,
Up:
#Top
Top
6 Other Resources for Learning About
sed
In addition to several books that have been written about
sed
(either specifically or as chapters in books which discuss
shell programming), one can find out more about
sed
(including suggestions of a few books) from the FAQ
for the
sed-users
mailing list, available from any of:
http://www.student.northpark.edu/pemente/sed/sedfaq.html
http://www.student.northpark.edu/pemente/sed/sedfaq.html
http://sed.sf.net/grabbag/tutorials/sedfaq.html
http://sed.sf.net/grabbag/tutorials/sedfaq.html
Also of interest are
http://www.student.northpark.edu/pemente/sed/index.htm
http://www.student.northpark.edu/pemente/sed/index.htm
and
http://sed.sf.net/grabbag
http://sed.sf.net/grabbag
,
which include
sed
tutorials and other
sed
-related goodies.
The
sed-users
mailing list itself maintained by Sven Guckes.
To subscribe, visit
http://groups.yahoo.com
http://groups.yahoo.com
and search
for the
sed-users
mailing list.
Next:
#Extended-regexps
Extended regexps
,
Previous:
#Other-Resources
Other Resources
,
Up:
#Top
Top
7 Reporting Bugs
Email bug reports to
mailto:bonzini@gnu.org
bonzini@gnu.org
.
Be sure to include the word “sed” somewhere in the
Subject:
field.
Also, please include the output of `
sed --version
' in the body
of your report if at all possible.
Please do not send a bug report like this:
while building frobme-1.3.4
$ configure
error--> sed: file sedscr line 1: Unknown option to 's'
If
GNU
sed
doesn't configure your favorite package, take a
few extra minutes to identify the specific problem and make a stand-alone
test case.  Unlike other programs such as C compilers, making such test
cases for
sed
is quite simple.
A stand-alone test case includes all the data necessary to perform the
test, and the specific invocation of
sed
that causes the problem.
The smaller a stand-alone test case is, the better.  A test case should
not involve something as far removed from
sed
as “try to configure
frobme-1.3.4”.  Yes, that is in principle enough information to look
for the bug, but that is not a very practical prospect.
Here are a few commonly reported bugs that are not bugs.
N
command on the last line
Most versions of
sed
exit without printing anything when
the
N
command is issued on the last line of a file.
GNU
sed
prints pattern space before exiting unless of course
the
-n
command switch has been specified.  This choice is
by design.
For example, the behavior of
sed N foo bar
would depend on whether foo has an even or an odd number of
lines
#fn-10
10
.  Or, when writing a script to read the
next few lines following a pattern match, traditional
implementations of
sed
would force you to write
something like
/foo/{ $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N; $!N }
instead of just
/foo/{ N;N;N;N;N;N;N;N;N; }
In any case, the simplest workaround is to use
$d;N
in
scripts that rely on the traditional behavior, or to set
the
POSIXLY_CORRECT
variable to a non-empty value.
Regex syntax clashes (problems with backslashes)
sed
uses the
posix
basic regular expression syntax.  According to
the standard, the meaning of some escape sequences is undefined in
this syntax;  notable in the case of
sed
are
\|
,
\+
,
\?
,
\`
,
\'
,
\<
,
\>
,
\b
,
\B
,
\w
, and
\W
.
As in all
GNU
programs that use
posix
basic regular
expressions,
sed
interprets these escape sequences as special
characters.  So,
x\+
matches one or more occurrences of `
x
'.
abc\|def
matches either `
abc
' or `
def
'.
This syntax may cause problems when running scripts written for other
sed
s.  Some
sed
programs have been written with the
assumption that
\|
and
\+
match the literal characters
|
and
+
.  Such scripts must be modified by removing the
spurious backslashes if they are to be used with modern implementations
of
sed
, like
GNU
sed
.
On the other hand, some scripts use s|abc\|def||g to remove occurrences
of
either
abc
or
def
.  While this worked until
sed
4.0.x, newer versions interpret this as removing the
string
abc|def
.  This is again undefined behavior according to
POSIX
, and this interpretation is arguably more robust: older
sed
s, for example, required that the regex matcher parsed
\/
as
/
in the common case of escaping a slash, which is
again undefined behavior; the new behavior avoids this, and this is good
because the regex matcher is only partially under our control.
In addition, this version of
sed
supports several escape characters
(some of which are multi-character) to insert non-printable characters
in scripts (
\a
,
\c
,
\d
,
\o
,
\r
,
\t
,
\v
,
\x
).  These can cause similar problems
with scripts written for other
sed
s.
-i
clobbers read-only files
In short, `
sed -i
' will let you delete the contents of
a read-only file, and in general the
-i
option
(see
#Invoking-sed
Invocation
) lets you clobber
protected files.  This is not a bug, but rather a consequence
of how the Unix filesystem works.
The permissions on a file say what can happen to the data
in that file, while the permissions on a directory say what can
happen to the list of files in that directory.  `
sed -i
'
will not ever open for writing  a file that is already on disk.
Rather, it will work on a temporary file that is finally renamed
to the original name: if you rename or delete files, you're actually
modifying the contents of the directory, so the operation depends on
the permissions of the directory, not of the file.  For this same
reason,
sed
does not let you use
-i
on a writeable file
in a read-only directory (but unbelievably nobody reports that as a
bug
...
).
0a
does not work (gives an error)
There is no line 0.  0 is a special address that is only used to treat
addresses like
0,/
RE
/
as active when the script starts: if
you write
1,/abc/d
and the first line includes the word `
abc
',
then that match would be ignored because address ranges must span at least
two lines (barring the end of the file); but what you probably wanted is
to delete every line up to the first one including `
abc
', and this
is obtained with
0,/abc/d
.
[a-z]
is case insensitive
You are encountering problems with locales.  POSIX mandates that
[a-z]
uses the current locale's collation order – in C parlance, that means using
strcoll(3)
instead of
strcmp(3)
.  Some locales have a
case-insensitive collation order, others don't: one of those that have
problems is Estonian.
Another problem is that
[a-z]
tries to use collation symbols.
This only happens if you are on the
GNU
system, using
GNU
libc's regular expression matcher instead of compiling the
one supplied with
GNU
sed.  In a Danish locale, for example,
the regular expression
^[a-z]$
matches the string `
aa
',
because this is a single collating symbol that comes after `
a
'
and before `
b
'; `
ll
' behaves similarly in Spanish
locales, or `
ij
' in Dutch locales.
To work around these problems, which may cause bugs in shell scripts, set
the
LC_COLLATE
and
LC_CTYPE
environment variables to `
C
'.
Next:
#Concept-Index
Concept Index
,
Previous:
#Reporting-Bugs
Reporting Bugs
,
Up:
#Top
Top
Appendix A Extended regular expressions
The only difference between basic and extended regular expressions is in
the behavior of a few characters: `
?
', `
+
', parentheses,
and braces (`
{}
').  While basic regular expressions require
these to be escaped if you want them to behave as special characters,
when using extended regular expressions you must escape them if
you want them
to match a literal character
.
Examples:
abc?
becomes `
abc\?
' when using extended regular expressions.  It matches
the literal string `
abc?
'.
c\+
becomes `
c+
' when using extended regular expressions.  It matches
one or more `
c
's.
a\{3,\}
becomes `
a{3,}
' when using extended regular expressions.  It matches
three or more `
a
's.
\(abc\)\{2,3\}
becomes `
(abc){2,3}
' when using extended regular expressions.  It
matches either `
abcabc
' or `
abcabcabc
'.
\(abc*\)\1
becomes `
(abc*)\1
' when using extended regular expressions.
Backreferences must still be escaped when using extended regular
expressions.
Next:
#Command-and-Option-Index
Command and Option Index
,
Previous:
#Extended-regexps
Extended regexps
,
Up:
#Top
Top
Concept Index
This is a general index of all issues discussed in this manual, with the
exception of the
sed
commands and command-line options.
#index-Additional-reading-about-_0040command_007bsed_007d-213
Additional reading about
sed
:
#Other-Resources
Other Resources
#index-g_t_0040var_007baddr1_007d_002c_002bN-63
addr1
,+N
:
#Addresses
Addresses
#index-g_t_0040var_007baddr1_007d_002c_007eN-64
addr1
,~N
:
#Addresses
Addresses
#index-Address_002c-as-a-regular-expression-51
Address, as a regular expression
:
#Addresses
Addresses
#index-Address_002c-last-line-48
Address, last line
:
#Addresses
Addresses
#index-Address_002c-numeric-45
Address, numeric
:
#Addresses
Addresses
#index-Addresses_002c-in-_0040command_007bsed_007d-scripts-42
Addresses, in
sed
scripts
:
#Addresses
Addresses
#index-Append-hold-space-to-pattern-space-166
Append hold space to pattern space
:
#Other-Commands
Other Commands
#index-Append-next-input-line-to-pattern-space-151
Append next input line to pattern space
:
#Other-Commands
Other Commands
#index-Append-pattern-space-to-hold-space-159
Append pattern space to hold space
:
#Other-Commands
Other Commands
#index-Appending-text-after-a-line-122
Appending text after a line
:
#Other-Commands
Other Commands
#index-Backreferences_002c-in-regular-expressions-97
Backreferences, in regular expressions
:
#The-_0022s_0022-Command
The "s" Command
#index-Branch-to-a-label_002c-if-_0040code_007bs_002f_002f_002f_007d-failed-201
Branch to a label, if
s///
failed
:
#Extended-Commands
Extended Commands
#index-Branch-to-a-label_002c-if-_0040code_007bs_002f_002f_002f_007d-succeeded-178
Branch to a label, if
s///
succeeded
:
#Programming-Commands
Programming Commands
#index-Branch-to-a-label_002c-unconditionally-175
Branch to a label, unconditionally
:
#Programming-Commands
Programming Commands
#index-Buffer-spaces_002c-pattern-and-hold-38
Buffer spaces, pattern and hold
:
#Execution-Cycle
Execution Cycle
#index-Bugs_002c-reporting-214
Bugs, reporting
:
#Reporting-Bugs
Reporting Bugs
#index-Case_002dinsensitive-matching-116
Case-insensitive matching
:
#The-_0022s_0022-Command
The "s" Command
#index-Caveat-_002d_002d_002d-_0023n-on-first-line-83
Caveat — #n on first line
:
#Common-Commands
Common Commands
#index-Command-groups-96
Command groups
:
#Common-Commands
Common Commands
#index-Comments_002c-in-scripts-80
Comments, in scripts
:
#Common-Commands
Common Commands
#index-Conditional-branch-202
Conditional branch
:
#Extended-Commands
Extended Commands
#index-Conditional-branch-179
Conditional branch
:
#Programming-Commands
Programming Commands
#index-Copy-hold-space-into-pattern-space-162
Copy hold space into pattern space
:
#Other-Commands
Other Commands
#index-Copy-pattern-space-into-hold-space-155
Copy pattern space into hold space
:
#Other-Commands
Other Commands
#index-Delete-first-line-from-pattern-space-148
Delete first line from pattern space
:
#Other-Commands
Other Commands
#index-Disabling-autoprint_002c-from-command-line-9
Disabling autoprint, from command line
:
#Invoking-sed
Invoking sed
#index-empty-regular-expression-53
empty regular expression
:
#Addresses
Addresses
#index-Evaluate-Bourne_002dshell-commands-181
Evaluate Bourne-shell commands
:
#Extended-Commands
Extended Commands
#index-Evaluate-Bourne_002dshell-commands_002c-after-substitution-111
Evaluate Bourne-shell commands, after substitution
:
#The-_0022s_0022-Command
The "s" Command
#index-Exchange-hold-space-with-pattern-space-169
Exchange hold space with pattern space
:
#Other-Commands
Other Commands
#index-Excluding-lines-70
Excluding lines
:
#Addresses
Addresses
#index-Extended-regular-expressions_002c-choosing-22
Extended regular expressions, choosing
:
#Invoking-sed
Invoking sed
#index-Extended-regular-expressions_002c-syntax-224
Extended regular expressions, syntax
:
#Extended-regexps
Extended regexps
#index-Files-to-be-processed-as-input-34
Files to be processed as input
:
#Invoking-sed
Invoking sed
#index-Flow-of-control-in-scripts-171
Flow of control in scripts
:
#Programming-Commands
Programming Commands
#index-Global-substitution-102
Global substitution
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040file_007b_002fdev_002fstderr_007d-file-146
GNU
extensions,
/dev/stderr
file
:
#Other-Commands
Other Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040file_007b_002fdev_002fstderr_007d-file-110
GNU
extensions,
/dev/stderr
file
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040file_007b_002fdev_002fstdin_007d-file-198
GNU
extensions,
/dev/stdin
file
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040file_007b_002fdev_002fstdin_007d-file-142
GNU
extensions,
/dev/stdin
file
:
#Other-Commands
Other Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040file_007b_002fdev_002fstdout_007d-file-225
GNU
extensions,
/dev/stdout
file
:
#Footnotes
Footnotes
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040file_007b_002fdev_002fstdout_007d-file-145
GNU
extensions,
/dev/stdout
file
:
#Other-Commands
Other Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040file_007b_002fdev_002fstdout_007d-file-109
GNU
extensions,
/dev/stdout
file
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-_0040code_007b0_007d-address-66
GNU
extensions,
0
address
:
#Addresses
Addresses
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-0_002c_0040var_007baddr2_007d-addressing-67
GNU
extensions, 0,
addr2
addressing
:
#Addresses
Addresses
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-_0040var_007baddr1_007d_002c_002b_0040var_007bN_007d-addressing-68
GNU
extensions,
addr1
,+
N
addressing
:
#Addresses
Addresses
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-_0040var_007baddr1_007d_002c_007e_0040var_007bN_007d-addressing-69
GNU
extensions,
addr1
,~
N
addressing
:
#Addresses
Addresses
#index-g_t_0040value_007bSSEDEXT_007d_002c-branch-if-_0040code_007bs_002f_002f_002f_007d-failed-200
GNU
extensions, branch if
s///
failed
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-case-modifiers-in-_0040code_007bs_007d-commands-99
GNU
extensions, case modifiers in
s
commands
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040value_007bSSEDEXT_007d_002c-checking-for-their-presence-204
GNU
extensions, checking for their presence
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-disabling-18
GNU
extensions, disabling
:
#Invoking-sed
Invoking sed
#index-g_t_0040value_007bSSEDEXT_007d_002c-evaluating-Bourne_002dshell-commands-183
GNU
extensions, evaluating Bourne-shell commands
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-evaluating-Bourne_002dshell-commands-113
GNU
extensions, evaluating Bourne-shell commands
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-extended-regular-expressions-23
GNU
extensions, extended regular expressions
:
#Invoking-sed
Invoking sed
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-_0040code_007bg_007d-and-_0040var_007bnumber_007d-modifier-interaction-in-_0040code_007bs_007d-command-105
GNU
extensions,
g
and
number
modifier interaction in
s
command
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-_0040code_007bI_007d-modifier-115
GNU
extensions,
I
modifier
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-_0040code_007bI_007d-modifier-56
GNU
extensions,
I
modifier
:
#Addresses
Addresses
#index-g_t_0040value_007bSSEDEXT_007d_002c-in_002dplace-editing-222
GNU
extensions, in-place editing
:
#Reporting-Bugs
Reporting Bugs
#index-g_t_0040value_007bSSEDEXT_007d_002c-in_002dplace-editing-13
GNU
extensions, in-place editing
:
#Invoking-sed
Invoking sed
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040code_007bL_007d-command-189
GNU
extensions,
L
command
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040code_007bM_007d-modifier-117
GNU
extensions,
M
modifier
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040value_007bSSEDEXT_007d_002c-modifiers-and-the-empty-regular-expression-54
GNU
extensions, modifiers and the empty regular expression
:
#Addresses
Addresses
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-_0040samp_007b_0040var_007bn_007d_007e_0040var_007bm_007d_007d-addresses-47
GNU
extensions, `
n
~
m
' addresses
:
#Addresses
Addresses
#index-g_t_0040value_007bSSEDEXT_007d_002c-quitting-silently-191
GNU
extensions, quitting silently
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-_0040code_007bR_007d-command-197
GNU
extensions,
R
command
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-reading-a-file-a-line-at-a-time-196
GNU
extensions, reading a file a line at a time
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-reformatting-paragraphs-188
GNU
extensions, reformatting paragraphs
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-returning-an-exit-code-192
GNU
extensions, returning an exit code
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-returning-an-exit-code-85
GNU
extensions, returning an exit code
:
#Common-Commands
Common Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-setting-line-length-138
GNU
extensions, setting line length
:
#Other-Commands
Other Commands
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-special-escapes-220
GNU
extensions, special escapes
:
#Reporting-Bugs
Reporting Bugs
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-special-escapes-209
GNU
extensions, special escapes
:
#Escapes
Escapes
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-special-two_002daddress-forms-65
GNU
extensions, special two-address forms
:
#Addresses
Addresses
#index-g_t_0040value_007bSSEDEXT_007d_002c-subprocesses-184
GNU
extensions, subprocesses
:
#Extended-Commands
Extended Commands
#index-g_t_0040value_007bSSEDEXT_007d_002c-subprocesses-114
GNU
extensions, subprocesses
:
#The-_0022s_0022-Command
The "s" Command
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-to-basic-regular-expressions-218
GNU
extensions, to basic regular expressions
:
#Reporting-Bugs
Reporting Bugs
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-to-basic-regular-expressions-72
GNU
extensions, to basic regular expressions
:
#Regular-Expressions
Regular Expressions
#index-g_t_0040value_007bSSEDEXT_007d_002c-two-addresses-supported-by-most-commands-120
GNU
extensions, two addresses supported by most commands
:
#Other-Commands
Other Commands
#index-g_t_0040acronym_007bGNU_007d-extensions_002c-unlimited-line-length-211
GNU
extensions, unlimited line length
:
#Limitations
Limitations
#index-g_t_0040value_007bSSEDEXT_007d_002c-writing-first-line-to-a-file-208
GNU
extensions, writing first line to a file
:
#Extended-Commands
Extended Commands
#index-Goto_002c-in-scripts-176
Goto, in scripts
:
#Programming-Commands
Programming Commands
#index-Greedy-regular-expression-matching-78
Greedy regular expression matching
:
#Regular-Expressions
Regular Expressions
#index-Grouping-commands-95
Grouping commands
:
#Common-Commands
Common Commands
#index-Hold-space_002c-appending-from-pattern-space-160
Hold space, appending from pattern space
:
#Other-Commands
Other Commands
#index-Hold-space_002c-appending-to-pattern-space-167
Hold space, appending to pattern space
:
#Other-Commands
Other Commands
#index-Hold-space_002c-copy-into-pattern-space-164
Hold space, copy into pattern space
:
#Other-Commands
Other Commands
#index-Hold-space_002c-copying-pattern-space-into-157
Hold space, copying pattern space into
:
#Other-Commands
Other Commands
#index-Hold-space_002c-definition-41
Hold space, definition
:
#Execution-Cycle
Execution Cycle
#index-Hold-space_002c-exchange-with-pattern-space-170
Hold space, exchange with pattern space
:
#Other-Commands
Other Commands
#index-In_002dplace-editing-221
In-place editing
:
#Reporting-Bugs
Reporting Bugs
#index-In_002dplace-editing_002c-activating-12
In-place editing, activating
:
#Invoking-sed
Invoking sed
#index-In_002dplace-editing_002c-Perl_002dstyle-backup-file-names-14
In-place editing, Perl-style backup file names
:
#Invoking-sed
Invoking sed
#index-Inserting-text-before-a-line-126
Inserting text before a line
:
#Other-Commands
Other Commands
#index-Labels_002c-in-scripts-173
Labels, in scripts
:
#Programming-Commands
Programming Commands
#index-Last-line_002c-selecting-49
Last line, selecting
:
#Addresses
Addresses
#index-Line-length_002c-setting-137
Line length, setting
:
#Other-Commands
Other Commands
#index-Line-length_002c-setting-17
Line length, setting
:
#Invoking-sed
Invoking sed
#index-Line-number_002c-printing-133
Line number, printing
:
#Other-Commands
Other Commands
#index-Line-selection-43
Line selection
:
#Addresses
Addresses
#index-Line_002c-selecting-by-number-46
Line, selecting by number
:
#Addresses
Addresses
#index-Line_002c-selecting-by-regular-expression-match-52
Line, selecting by regular expression match
:
#Addresses
Addresses
#index-Line_002c-selecting-last-50
Line, selecting last
:
#Addresses
Addresses
#index-List-pattern-space-135
List pattern space
:
#Other-Commands
Other Commands
#index-Mixing-_0040code_007bg_007d-and-_0040var_007bnumber_007d-modifiers-in-the-_0040code_007bs_007d-command-106
Mixing
g
and
number
modifiers in the
s
command
:
#The-_0022s_0022-Command
The "s" Command
#index-Next-input-line_002c-append-to-pattern-space-150
Next input line, append to pattern space
:
#Other-Commands
Other Commands
#index-Next-input-line_002c-replace-pattern-space-with-92
Next input line, replace pattern space with
:
#Common-Commands
Common Commands
#index-Non_002dbugs_002c-in_002dplace-editing-223
Non-bugs, in-place editing
:
#Reporting-Bugs
Reporting Bugs
#index-Non_002dbugs_002c-_0040code_007bN_007d-command-on-the-last-line-216
Non-bugs,
N
command on the last line
:
#Reporting-Bugs
Reporting Bugs
#index-Non_002dbugs_002c-regex-syntax-clashes-219
Non-bugs, regex syntax clashes
:
#Reporting-Bugs
Reporting Bugs
#index-Parenthesized-substrings-98
Parenthesized substrings
:
#The-_0022s_0022-Command
The "s" Command
#index-Pattern-space_002c-definition-40
Pattern space, definition
:
#Execution-Cycle
Execution Cycle
#index-Perl_002dstyle-regular-expressions_002c-multiline-57
Perl-style regular expressions, multiline
:
#Addresses
Addresses
#index-Portability_002c-comments-81
Portability, comments
:
#Common-Commands
Common Commands
#index-Portability_002c-line-length-limitations-212
Portability, line length limitations
:
#Limitations
Limitations
#index-Portability_002c-_0040code_007bN_007d-command-on-the-last-line-215
Portability,
N
command on the last line
:
#Reporting-Bugs
Reporting Bugs
#index-g_t_0040code_007bPOSIXLY_005fCORRECT_007d-behavior_002c-bracket-expressions-76
POSIXLY_CORRECT
behavior, bracket expressions
:
#Regular-Expressions
Regular Expressions
#index-g_t_0040code_007bPOSIXLY_005fCORRECT_007d-behavior_002c-enabling-19
POSIXLY_CORRECT
behavior, enabling
:
#Invoking-sed
Invoking sed
#index-g_t_0040code_007bPOSIXLY_005fCORRECT_007d-behavior_002c-escapes-210
POSIXLY_CORRECT
behavior, escapes
:
#Escapes
Escapes
#index-g_t_0040code_007bPOSIXLY_005fCORRECT_007d-behavior_002c-_0040code_007bN_007d-command-217
POSIXLY_CORRECT
behavior,
N
command
:
#Reporting-Bugs
Reporting Bugs
#index-Print-first-line-from-pattern-space-153
Print first line from pattern space
:
#Other-Commands
Other Commands
#index-Printing-line-number-132
Printing line number
:
#Other-Commands
Other Commands
#index-Printing-text-unambiguously-136
Printing text unambiguously
:
#Other-Commands
Other Commands
#index-Quitting-193
Quitting
:
#Extended-Commands
Extended Commands
#index-Quitting-86
Quitting
:
#Common-Commands
Common Commands
#index-Range-of-lines-58
Range of lines
:
#Addresses
Addresses
#index-Range-with-start-address-of-zero-61
Range with start address of zero
:
#Addresses
Addresses
#index-Read-next-input-line-93
Read next input line
:
#Common-Commands
Common Commands
#index-Read-text-from-a-file-195
Read text from a file
:
#Extended-Commands
Extended Commands
#index-Read-text-from-a-file-141
Read text from a file
:
#Other-Commands
Other Commands
#index-Reformat-pattern-space-186
Reformat pattern space
:
#Extended-Commands
Extended Commands
#index-Reformatting-paragraphs-187
Reformatting paragraphs
:
#Extended-Commands
Extended Commands
#index-Replace-hold-space-with-copy-of-pattern-space-156
Replace hold space with copy of pattern space
:
#Other-Commands
Other Commands
#index-Replace-pattern-space-with-copy-of-hold-space-163
Replace pattern space with copy of hold space
:
#Other-Commands
Other Commands
#index-Replacing-all-text-matching-regexp-in-a-line-103
Replacing all text matching regexp in a line
:
#The-_0022s_0022-Command
The "s" Command
#index-Replacing-only-_0040var_007bn_007dth-match-of-regexp-in-a-line-104
Replacing only
n
th match of regexp in a line
:
#The-_0022s_0022-Command
The "s" Command
#index-Replacing-selected-lines-with-other-text-129
Replacing selected lines with other text
:
#Other-Commands
Other Commands
#index-Requiring-_0040value_007bSSED_007d-205
Requiring
GNU
sed
:
#Extended-Commands
Extended Commands
#index-Script-structure-37
Script structure
:
#sed-Programs
sed Programs
#index-Script_002c-from-a-file-33
Script, from a file
:
#Invoking-sed
Invoking sed
#index-Script_002c-from-command-line-30
Script, from command line
:
#Invoking-sed
Invoking sed
#index-g_t_0040command_007bsed_007d-program-structure-36
sed
program structure
:
#sed-Programs
sed Programs
#index-Selecting-lines-to-process-44
Selecting lines to process
:
#Addresses
Addresses
#index-Selecting-non_002dmatching-lines-71
Selecting non-matching lines
:
#Addresses
Addresses
#index-Several-lines_002c-selecting-59
Several lines, selecting
:
#Addresses
Addresses
#index-Slash-character_002c-in-regular-expressions-55
Slash character, in regular expressions
:
#Addresses
Addresses
#index-Spaces_002c-pattern-and-hold-39
Spaces, pattern and hold
:
#Execution-Cycle
Execution Cycle
#index-Special-addressing-forms-60
Special addressing forms
:
#Addresses
Addresses
#index-Standard-input_002c-processing-as-input-35
Standard input, processing as input
:
#Invoking-sed
Invoking sed
#index-Stream-editor-1
Stream editor
:
#Introduction
Introduction
#index-Subprocesses-182
Subprocesses
:
#Extended-Commands
Extended Commands
#index-Subprocesses-112
Subprocesses
:
#The-_0022s_0022-Command
The "s" Command
#index-Substitution-of-text_002c-options-101
Substitution of text, options
:
#The-_0022s_0022-Command
The "s" Command
#index-Text_002c-appending-123
Text, appending
:
#Other-Commands
Other Commands
#index-Text_002c-deleting-88
Text, deleting
:
#Common-Commands
Common Commands
#index-Text_002c-insertion-127
Text, insertion
:
#Other-Commands
Other Commands
#index-Text_002c-printing-90
Text, printing
:
#Common-Commands
Common Commands
#index-Text_002c-printing-after-substitution-107
Text, printing after substitution
:
#The-_0022s_0022-Command
The "s" Command
#index-Text_002c-writing-to-a-file-after-substitution-108
Text, writing to a file after substitution
:
#The-_0022s_0022-Command
The "s" Command
#index-Transliteration-119
Transliteration
:
#Other-Commands
Other Commands
#index-Unbuffered-I_002fO_002c-choosing-27
Unbuffered I/O, choosing
:
#Invoking-sed
Invoking sed
#index-Usage-summary_002c-printing-5
Usage summary, printing
:
#Invoking-sed
Invoking sed
#index-Version_002c-printing-3
Version, printing
:
#Invoking-sed
Invoking sed
#index-Working-on-separate-files-24
Working on separate files
:
#Invoking-sed
Invoking sed
#index-Write-first-line-to-a-file-207
Write first line to a file
:
#Extended-Commands
Extended Commands
#index-Write-to-a-file-144
Write to a file
:
#Other-Commands
Other Commands
#index-Zero_002c-as-range-start-address-62
Zero, as range start address
:
#Addresses
Addresses
Previous:
#Concept-Index
Concept Index
,
Up:
#Top
Top
Command and Option Index
This is an alphabetical list of all
sed
commands and command-line
options.
#index-g_t_0023-_0028comments_0029-79
# (comments)
:
#Common-Commands
Common Commands
#index-g_t_002d_002dexpression-29
--expression
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dfile-32
--file
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dhelp-4
--help
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002din_002dplace-11
--in-place
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dline_002dlength-16
--line-length
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dquiet-7
--quiet
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dregexp_002dextended-21
--regexp-extended
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dsilent-8
--silent
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dunbuffered-26
--unbuffered
:
#Invoking-sed
Invoking sed
#index-g_t_002d_002dversion-2
--version
:
#Invoking-sed
Invoking sed
#index-g_t_002de-28
-e
:
#Invoking-sed
Invoking sed
#index-g_t_002df-31
-f
:
#Invoking-sed
Invoking sed
#index-g_t_002di-10
-i
:
#Invoking-sed
Invoking sed
#index-g_t_002dl-15
-l
:
#Invoking-sed
Invoking sed
#index-g_t_002dn-6
-n
:
#Invoking-sed
Invoking sed
#index-g_t_002dn_002c-forcing-from-within-a-script-82
-n, forcing from within a script
:
#Common-Commands
Common Commands
#index-g_t_002dr-20
-r
:
#Invoking-sed
Invoking sed
#index-g_t_002du-25
-u
:
#Invoking-sed
Invoking sed
#index-g_t_003a-_0028label_0029-command-172
: (label) command
:
#Programming-Commands
Programming Commands
#index-g_t_003d-_0028print-line-number_0029-command-131
= (print line number) command
:
#Other-Commands
Other Commands
#index-a-_0028append-text-lines_0029-command-121
a (append text lines) command
:
#Other-Commands
Other Commands
#index-b-_0028branch_0029-command-174
b (branch) command
:
#Programming-Commands
Programming Commands
#index-c-_0028change-to-text-lines_0029-command-128
c (change to text lines) command
:
#Other-Commands
Other Commands
#index-D-_0028delete-first-line_0029-command-147
D (delete first line) command
:
#Other-Commands
Other Commands
#index-d-_0028delete_0029-command-87
d (delete) command
:
#Common-Commands
Common Commands
#index-e-_0028evaluate_0029-command-180
e (evaluate) command
:
#Extended-Commands
Extended Commands
#index-G-_0028appending-Get_0029-command-165
G (appending Get) command
:
#Other-Commands
Other Commands
#index-g-_0028get_0029-command-161
g (get) command
:
#Other-Commands
Other Commands
#index-H-_0028append-Hold_0029-command-158
H (append Hold) command
:
#Other-Commands
Other Commands
#index-h-_0028hold_0029-command-154
h (hold) command
:
#Other-Commands
Other Commands
#index-i-_0028insert-text-lines_0029-command-125
i (insert text lines) command
:
#Other-Commands
Other Commands
#index-L-_0028fLow-paragraphs_0029-command-185
L (fLow paragraphs) command
:
#Extended-Commands
Extended Commands
#index-l-_0028list-unambiguously_0029-command-134
l (list unambiguously) command
:
#Other-Commands
Other Commands
#index-N-_0028append-Next-line_0029-command-149
N (append Next line) command
:
#Other-Commands
Other Commands
#index-n-_0028next_002dline_0029-command-91
n (next-line) command
:
#Common-Commands
Common Commands
#index-P-_0028print-first-line_0029-command-152
P (print first line) command
:
#Other-Commands
Other Commands
#index-p-_0028print_0029-command-89
p (print) command
:
#Common-Commands
Common Commands
#index-q-_0028quit_0029-command-84
q (quit) command
:
#Common-Commands
Common Commands
#index-Q-_0028silent-Quit_0029-command-190
Q (silent Quit) command
:
#Extended-Commands
Extended Commands
#index-r-_0028read-file_0029-command-140
r (read file) command
:
#Other-Commands
Other Commands
#index-R-_0028read-line_0029-command-194
R (read line) command
:
#Extended-Commands
Extended Commands
#index-s-command_002c-option-flags-100
s command, option flags
:
#The-_0022s_0022-Command
The "s" Command
#index-T-_0028test-and-branch-if-failed_0029-command-199
T (test and branch if failed) command
:
#Extended-Commands
Extended Commands
#index-t-_0028test-and-branch-if-successful_0029-command-177
t (test and branch if successful) command
:
#Programming-Commands
Programming Commands
#index-v-_0028version_0029-command-203
v (version) command
:
#Extended-Commands
Extended Commands
#index-w-_0028write-file_0029-command-143
w (write file) command
:
#Other-Commands
Other Commands
#index-W-_0028write-first-line_0029-command-206
W (write first line) command
:
#Extended-Commands
Extended Commands
#index-x-_0028eXchange_0029-command-168
x (eXchange) command
:
#Other-Commands
Other Commands
#index-y-_0028transliterate_0029-command-118
y (transliterate) command
:
#Other-Commands
Other Commands
#index-g_t_0040_007b_0040_007d-command-grouping-94
{} command grouping
:
#Common-Commands
Common Commands
Table of Contents
#Top
sed, a stream editor
#Introduction
1 Introduction
#Invoking-sed
2 Invocation
#sed-Programs
3
sed
Programs
#Execution-Cycle
3.1 How
sed
Works
#Addresses
3.2 Selecting lines with
sed
#Regular-Expressions
3.3 Overview of Regular Expression Syntax
#Common-Commands
3.4 Often-Used Commands
#The-_0022s_0022-Command
3.5 The
s
Command
#Other-Commands
3.6 Less Frequently-Used Commands
#Programming-Commands
3.7 Commands for
sed
gurus
#Extended-Commands
3.8 Commands Specific to
GNU
sed
#Escapes
3.9
GNU
Extensions for Escapes in Regular Expressions
#Examples
4 Some Sample Scripts
#Centering-lines
4.1 Centering Lines
#Increment-a-number
4.2 Increment a Number
#Rename-files-to-lower-case
4.3 Rename Files to Lower Case
#Print-bash-environment
4.4 Print
bash
Environment
#Reverse-chars-of-lines
4.5 Reverse Characters of Lines
#tac
4.6 Reverse Lines of Files
#cat-_002dn
4.7 Numbering Lines
#cat-_002db
4.8 Numbering Non-blank Lines
#wc-_002dc
4.9 Counting Characters
#wc-_002dw
4.10 Counting Words
#wc-_002dl
4.11 Counting Lines
#head
4.12 Printing the First Lines
#tail
4.13 Printing the Last Lines
#uniq
4.14 Make Duplicate Lines Unique
#uniq-_002dd
4.15 Print Duplicated Lines of Input
#uniq-_002du
4.16 Remove All Duplicated Lines
#cat-_002ds
4.17 Squeezing Blank Lines
#Limitations
5
GNU
sed
's Limitations and Non-limitations
#Other-Resources
6 Other Resources for Learning About
sed
#Reporting-Bugs
7 Reporting Bugs
#Extended-regexps
Appendix A Extended regular expressions
#Concept-Index
Concept Index
#Command-and-Option-Index
Command and Option Index
Footnotes
[
#fnd-1
1
]
This applies to commands such as
=
,
a
,
c
,
i
,
l
,
p
.  You can
still write to the standard output by using the
w
or
W
commands together with the
/dev/stdout
special file
[
#fnd-2
2
]
Note that
GNU
sed
creates the backup
file whether or not any output is actually changed.
[
#fnd-3
3
]
Actually,
if
sed
prints a line without the terminating newline, it will
nevertheless print the missing newline as soon as more text is sent to
the same output stream, which gives the “least expected surprise”
even though it does not make commands like `
sed -n p
' exactly
identical to
cat
.
[
#fnd-4
4
]
This is equivalent to
p
unless the
-i
option is being used.
[
#fnd-5
5
]
This is equivalent to
p
unless the
-i
option is being used.
[
#fnd-6
6
]
All
the escapes introduced here are
GNU
extensions, with the exception of
\n
.  In basic regular
expression mode, setting
POSIXLY_CORRECT
disables them inside
bracket expressions.
[
#fnd-7
7
]
sed
guru Greg
Ubben wrote an implementation of the
dc
rpn
calculator!
It is distributed together with sed.
[
#fnd-8
8
]
This requires
another script to pad the output of banner; for example
#! /bin/sh
banner -w $1 $2 $3 $4 |
sed -e :a -e '/^.\{0,'$1'\}$/ { s/$/ /; ba; }' |
~/sedscripts/reverseline.sed
[
#fnd-9
9
]
Some implementations
have a limit of 199 commands per script
[
#fnd-10
10
]
which is the actual “bug” that prompted the
change in behavior
