Shell Programming and Scripting

trap [Command] [Signal] ... Runs the specified command when the shell receives the specified signal or signals. The Command parameter is read once when the trap is set and once when the trap is taken. The Signal parameter can be given as a number or as the name of the signal. Trap commands are executed in order of signal number. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective.

If the command is -, all traps are reset to their original values. If you omit the command and the first signal is a numeric signal number, then the ksh command resets the value of the Signal parameter or parameters to the original values.

Note: If you omit the command and the first signal is a symbolic name, the signal is interpreted as a command.

If the value of the Signal parameter is the ERR signal, the specified command is carried out whenever a command has a nonzero exit status. If the signal is DEBUG, then the specified command is carried out after each command. If the value of the Signal parameter is the 0 or EXIT signal and the trap command is executed inside the body of a function, the specified command is carried out after the function completes. If the Signal parameter is 0 or EXIT for a trap command set outside any function, the specified command is carried out on exit from the shell. The trap command with no arguments prints a list of commands associated with each signal number.

For a complete list of Signal parameter values used in the trap command without the SIG prefix, see the sigaction, sigvec, or signal subroutine in the AIX 5L Version 5.3 Technical Reference: Base Operating System and Extensions Volume 2.