trap

Execute a command when the shell receives a signal.

Syntax
      trap [-lp] [[arg] sigspec ...]

Key
   -p   Display signal commands (or trap commands for sigspec)

   -l   Print a list of signal names and their corresponding numbers.

   arg  The command to be executed when the shell receives signal(s) sigspec.

If arg is absent (and there is a single sigspec) or -, each specified signal is reset to its original disposition (the value it had upon entrance to the shell).

If arg is the null string the signal specified by each sigspec is ignored by the shell and by the commands it invokes.

If arg is not present and -p has been supplied, then the trap commands associated with each sigspec are displayed. If no arguments are supplied or if only -p is given, trap prints the list of commands associated with each signal.

Each sigspec is either a signal name defined in <signal.h>, or a signal number. Signal names are case insensitive and the SIG prefix is optional.

If a sigspec is EXIT (0) the command arg is executed on exit from the shell.
If a sigspec is DEBUG, the command arg is executed before every simple command, for command, case command, select command, every arithmetic for command, and before the first command executes in a shell function (see SHELL GRAMMAR). Refer to the description of the extdebug option to the shopt builtin for details of its effect on the DEBUG trap.

If a sigspec is ERR, the command arg is executed whenever a simple command has a non-zero exit status, subject to the following conditions. The ERR trap is not executed if the failed command is part of the command list immediately following a while or until keyword, part of the test in an if statement, part of a && or || list, or if the command's return value is being inverted via !.
These are the same conditions obeyed by the errexit option.

If a sigspec is RETURN, the command arg is executed each time a shell function or a script executed with the . or source builtins finishes executing.

Signals ignored upon entry to the shell cannot be trapped or reset. Trapped signals that are not being ignored are reset to their original values in a
child process when it is created.

The return status is false if any sigspec is invalid; otherwise trap returns true.

trap is a bash built in command.

“When elephant steps on a trap, no more trap” ~ African Proverb

Related:

exec - Execute a command


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