Bash-Beginners-Guide

Chapter 12. Catching signals
In this chapter, we will discuss the following subjects:
12.1. Signals
♦ Available signals
♦ Use of the signals
♦ Use of the trap statement
♦ How to prevent users from interrupting your programs
12.1.1. Introduction
12.1.1.1. Finding the signal man page
Your system contains a man page listing all the available signals, but depending on your operating system, it
might be opened in a different way. On most Linux systems, this will be man 7 signal. When in doubt, locate
the exact man page and section using commands like
man -k signal | grep list
or
apropos signal | grep list
Signal names can be found using kill -l.
12.1.1.2. Signals to your Bash shell
In the absence of any traps, an interactive Bash shell ignores SIGTERM and SIGQUIT. SIGINT is caught and
handled, and if job control is active, SIGTTIN, SIGTTOU and SIGTSTP are also ignored. Commands that are
run as the result of a command substitution also ignore these signals, when keyboard generated.
SIGHUP by default exits a shell. An interactive shell will send a SIGHUP to all jobs, running or stopped; see
the documentation on the disown built-in if you want to disable this default behavior for a particular process.
Use the huponexit option for killing all jobs upon receiving a SIGHUP signal, using the shopt built-in.
12.1.1.3. Sending signals using the shell
The following signals can be sent using the Bash shell:
Table 12-1. Control signals in Bash
Standard key
combination
Ctrl+C
Meaning
The interrupt signal, sends SIGINT to the job running in the foreground.
Chapter 12. Catching signals 137