Advanced Bash−Scripting Guide

Example 9−2. Timed Input
Advanced Bash−Scripting Guide
#!/bin/bash
# timed−input.sh
# TMOUT=3 useless in a script
TIMELIMIT=3 # Three seconds in this instance, may be set to different value.
PrintAnswer()
{
if [ "$answer" = TIMEOUT ]
then
echo $answer
else # Don't want to mix up the two instances.
echo "Your favorite veggie is $answer"
kill $! # Kills no longer needed TimerOn function running in background.
# $! is PID of last job running in background.
fi
}
TimerOn()
{
sleep $TIMELIMIT && kill −s 14 $$ &
# Waits 3 seconds, then sends sigalarm to script.
}
Int14Vector()
{
answer="TIMEOUT"
PrintAnswer
exit 14
}
trap Int14Vector 14
# Timer interrupt (14) subverted for our purposes.
echo "What is your favorite vegetable "
TimerOn
read answer
PrintAnswer
# Admittedly, this is a kludgy implementation of timed input,
#+ however the "−t" option to "read" simplifies this task.
# See "t−out.sh", below.
# If you need something really elegant...
#+ consider writing the application in C or C++,
#+ using appropriate library functions, such as 'alarm' and 'setitimer'.
exit 0
An alternative is using stty.
Example 9−3. Once more, timed input
Chapter 9. Variables Revisited 71