       1msignal 22m?4m-restart24m? 4maction24m 4msiglist24m ?4mcommand24m?

              Warning:   If  signals are being used as an event source (a 1mtrap0m
              action), rather than generating an error to  terminate  a  task;
              one  must use the 1m-restart 22moption.  This causes a blocked system
              call, such as 1mread 22mor 1mwaitpid 22mto be restarted rather than gener-
              ate  an  error.   Failure  to  do this may results in unexpected
              errors when a signal arrives while in one of these system calls.
              When available, the 1m-restart 22moption can prevent this problem.

              If  1m-restart  22mis specified, restart blocking system calls rather
              than generating an error.  The signal will be handled  once  the
              Tcl command that issued the system call completes.  The 1m-restart0m
              options is not available on all operating systems  and  its  use
              will  generate  an  error  when  it is not supported.  Use 1minfox0m
              1mhave_signal_restart 22mto check for availability.

              Specify the action to take when a Unix  signal  is  received  by
              Extended Tcl, or a program that embeds it.  4mSiglist24m is a list of
              either the symbolic or numeric Unix signal (the  SIG  prefix  is
              optional).   4mAction24m  is  one of the following actions to be per-
              formed on receipt of the signal.  To specify all modifiable sig-
              nals,  use  `*'  (this  will not include SIGKILL and SIGSTOP, as
              they can not be modified).

              1mdefault0m
                     Perform system default action  when  signal  is  received
                     (see 1msignal 22msystem call documentation).

              1mignore 22mIgnore the signal.

              1merror  22mGenerate  a  catchable  Tcl  error.  It will be as if the
                     command that was running returned an  error.   The  error
                     code will be in the form:
                          1mPOSIX SIG 4m22msigname0m
                     For  the  death  of  child signal, 4msigname24m will always be
                     SIGCHLD, rather than SIGCLD, to  allow  writing  portable
                     code.

              1mtrap   22mWhen the signal occurs, execute 4mcommand24m and continue exe-
                     cution if an error is not returned by 4mcommand24m.  The  com-
                     mand will be executed in the global context.  The command
                     will be edited before execution, replacing occurrences of
                     "%S" with the signal name.  Occurrences of "%%" result in
                     a single "%".  This editing occurs just before  the  trap
                     command is evaluated.  If an error is returned, then fol-
                     low the standard Tcl error mechanism.  Often 4mcommand24m will
                     just do an 1mexit22m.

              1mget    22mRetrieve  the  current settings of the specified signals.
                     A keyed list will be returned were the keys  are  one  of
                     the  specified signals and the values are a list consist-
                     ing of the action associated with the signal, a 1m0 22mif  the
                     signal  may  be  delivered  (not  block) and a 1m1 22mif it is
                     blocked and a flag indicating  if  restarting  of  system
                     calls   is   specified.    The   actions   maybe  one  of
                     `1mdefault22m',`1mignore22m', `1merror22m' or `1mtrap22m'.  If the action  is
                     trap,  the  third  element is the command associated with
                     the action.  The action `1munknown22m' is returned if  a  non-
                     Tcl signal handler has been associated with the signal.

              1mset    22mSet  signals  from a keyed list in the format returned by
                     the 1mget22m.  For this action, 4msiglist24m is the keyed  list  of
                     signal  state.   Signals  with an action of `1munknown22m' are
                     not modified.

              1mblock  22mBlock the specified signals from being  received.  (Posix
                     systems only).

              1munblock0m
                     Allow  the  specified signal to be received. Pending sig-
                     nals will not occur. (Posix systems only).

              The signal action will remain enabled after the specified signal
              has occurred.  The exception to this is 1mSIGCHLD 22mon systems with-
              out Posix signals.  For these systems, 1mSIGCHLD 22mis not  be  auto-
              matically reenabled.  After a 1mSIGCHLD 22msignal is received, a call
              to 1mwait 22mmust be performed to retrieve the  exit  status  of  the
              child process before issuing another 1msignal SIGCHLD 4m22m...24m command.
              For code that is to be portable between both types  of  systems,
              use this approach.

              Signals  are not processed until after the completion of the Tcl
              command that is executing when the signal is  received.   If  an
              interactive Tcl shell is running, then the 1mSIGINT 22mwill be set to
              1merror22m, non-interactive Tcl sessions leave 1mSIGINT 22munchanged  from
              when  the  process started (normally 1mdefault 22mfor foreground pro-
              cesses and 1mignore 22mfor processes in the background).
