trap(1) 							   User Commands							   trap(1)

NAME

       trap, onintr - shell built-in functions to respond to (hardware) signals

SYNOPSIS

   sh
       trap [argument n [n2]...]

   csh
       onintr [-| label]

   ksh
       *trap [arg sig [sig2...]]

   ksh93
       +trap [-p] [action condition...]

DESCRIPTION

   sh
       The  trap command argument is to be read and executed when the shell receives numeric or symbolic signal(s) (n). (Note: argument is scanned
       once when the trap is set and once when the trap is taken.) Trap commands are executed in order of signal number or corresponding  symbolic
       names. Any attempt to set a trap on a signal that was ignored on entry to the current shell is ineffective. An attempt to trap on signal 11
       (memory fault) produces an error. If argument is absent all trap(s) n are reset to their original values. If argument is  the  null  string
       this  signal is ignored by the shell and by the commands it invokes. If n is 0 the command argument is executed on exit from the shell. The
       trap command with no arguments prints a list of commands associated with each signal number.

   csh
       onintr controls the action of the shell on interrupts. With no arguments, onintr restores the default action of the  shell  on  interrupts.
       (The  shell  terminates	shell  scripts and returns to the terminal command input level). With the - argument, the shell ignores all inter-
       rupts. With a label argument, the shell executes a goto label when an interrupt is received or a child process terminates  because  it  was
       interrupted.

   ksh
       trap uses arg as a command to be read and executed when the shell receives signal(s) sig. arg is scanned once when the trap is set and once
       when the trap is taken. Each sig can be specified 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 arg is omitted or is -,
       then the trap(s) for each sig are reset to their original values. If arg is the null (the empty string, for example, "") string	then  this
       signal  is  ignored by the shell and by the commands it invokes. If sig is ERR then arg are executed whenever a command has a non-zero exit
       status. If sig is DEBUG then arg are executed after each command. If sig is 0 or EXIT for a trap set outside any function then the  command
       arg is executed on exit from the shell. The trap command with no arguments prints a list of commands associated with each signal number.

       On this manual page, ksh(1) commands that are preceded by one or two * (asterisks) are treated specially in the following ways:

	   1.	  Variable assignment lists preceding the command remain in effect when the command completes.

	   2.	  I/O redirections are processed after variable assignments.

	   3.	  Errors cause a script that contains them to abort.

	   4.	  Words, following a command preceded by ** that are in the format of a variable assignment, are expanded with the same rules as a
		  variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file  name  genera-
		  tion are not performed.

   ksh93
       trap is a special built-in that defines actions to be taken when conditions such as receiving a signal occur. trap can also be used to dis-
       play the current trap settings on standard output.

       If action is -, trap resets each condition to the default value. If action is an empty string, the shell ignores each of the conditions	if
       they  arise. Otherwise, the argument action is read and executed by the shell as if it were processed by eval when one of the corresponding
       conditions arise. The action of the trap overrides any previous action associated with each specified condition. The value  of  $?  is  not
       altered by the trap execution.

       condition can be the name or number of a signal, or one of the following:

       EXIT	Execute  this  trap  when  the shell exits. If defined within a function with the function reserved word, executes the trap in the
		caller's environment when the function returns. The trap action is restored to the value it had when it called the function.

       0	Same as EXIT.

       DEBUG	Execute before each simple command is executed but after the arguments are expanded.

       ERR	Execute whenever set -e would cause the shell to exit.

       KEYBD	Execute when a key is entered from a terminal device.

       Signal names are case insensitive and the sig prefix is optional. Signals that were ignored on entry  to  a  non-interactive  shell  cannot
       trapped	or reset although doing so does not report an error. The use of signal numbers other than 1, 2, 3, 6, 9, 14, and 15 are not porta-
       ble.

       Although trap is a special built-in, specifying a condition that the shell does not know about causes trap to exit  with  a  non-zero  exit
       status, but does not terminate the invoking shell.

       If no action or conditions are specified then all the current trap settings are written to standard output.

       The following options are supported by the trap built-in command in ksh93:

       -p    Causes the current traps to be output in a format that can be processed as input to the shell to recreate the current traps.

       The trap built-in in ksh93 exits with one of the following values:

       0     Successful completion.

       >0    An error occurred.

       On this manual page, ksh93(1) commands that are preceded by one or two + (plus signs) are treated specially in the following ways:

	   1.	  Variable assignment lists preceding the command remain in effect when the command completes.

	   2.	  I/O redirections are processed after variable assignments.

	   3.	  Errors cause a script that contains them to abort.

	   4.	  They are not valid function names.

	   5.	  Words, following a command preceded by ++ that are in the format of a variable assignment, are expanded with the same rules as a
		  variable assignment. This means that tilde substitution is performed after the = sign and word splitting and file  name  genera-
		  tion are not performed.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), eval(1), exit(1), ksh(1), ksh93(1), sh(1), attributes(5)

SunOS 5.11							    20 Nov 2007 							   trap(1)