Shells allow you to concatenate and group commands for conditional execution. Each command returns an exit code which determines the success or failure of its operation. If it is 0 (zero) the command was successful, everything else marks an error which is specific to the command.
The following list shows, how commands can be grouped:
Command1 ; Command2
executes the commands in sequential order. The exit code is not checked. The following line displays the content of the file with cat and then prints its file properties with ls regardless of their exit codes:
cat filelist.txt ; ls -l filelist.txt
Command1 && Command2
runs the right command, if the left command was successful (logical AND). The following line displays the content of the file and prints its file properties only, when the previous command was successful (compare it with the previous entry in this list):
cat filelist.txt && ls -l filelist.txt
Command1 || Command2
runs the right command, when the left command has failed (logical OR).
The following line creates only a directory in
/home/wilber/bar when the creation of the
directory in /home/tux/foo has failed:
mkdir /home/tux/foo || mkdir /home/wilber/bar
funcname(){ ... }
creates a shell function. You can use the positional parameters to
access its arguments. The following line defines the function
hello to print a short message:
hello() { echo "Hello $1"; }You can call this function like this:
hello Tux
which prints:
Hello Tux