RE: Traps...

[Vázquez, Gustavo <GustavoV@correo.com.uy>]

	El mail inicial era mio, y con la urgencia que tenia de usar esos
conocimientos, busque en el Web informacion ( no tengo instalada la pagina
man del comando trap en mi sistema, y encontre la siguiente página:

	 <<node41>> 
	Espero que sirva de ayuda como me sirvio a mi.

	Saludos
	Gustavo

	------------------------------

> En un reciente mensaje, he leido lo de poner traps a la ejecución de un
> programa para no conseguir acceso a una shell... ¿alguien es tan amable de
> explicarme qué es ésto, cómo funciona, con qué lenguajes puedo hacerlo, y
> algún ejemplillo?
>

Title: trap: Trap signals

Next: Tips Using Shell Commands Up: Programming the Shell Previous: set: Change Command-line Parameters

trap: Trap signals

Processes may be sent signals using either the kill command, or a control key combination such as CTRL-C. The interrupt signal (CTRL-C) usually kills the process.

Table taken from [6, p. 883,] shows some of the signals used in Shell Programming.

  
Table: Signal numbers for trap command.

The trap command typically appears as one of the first lines in the shell script. It contains the commands to be executed when a signal is detected as well as what signals to trap.

#!/bin/sh
TMPFILE=/usr/tmp/junk.$$
trap 'rm -f $TMPFILE; exit 0' 1 2 15 
.
.
.

Upon receiving signals 1, 2 or 15, $TMPFILE would be deleted and the script would terminate the shell script normally. This shows how trap may be used to clean up before exiting.

#!/bin/sh
TMPFILE=/usr/tmp/junk.$$
trap '' 0 1 2
.
.
.

The above example shows how trap may be used to ignore specific signals (0, 1 and 2).

NOTE that when the signal is received, the command currently being executed is interrupted, and execution flow continues at the next line of the script.

---

Claude Cantin
Sun Apr 11 02:10:52 EDT 1999