Bash-Beginners-Guide

Bash Guide for Beginners
9.2.2. Examples
9.2.2.1. Simple example using while
Here is an example for the impatient:
#!/bin/bash
# This script opens 4 terminal windows.
i="0"
while [ $i -lt 4 ]
do
xterm &
i=$[$i+1]
done
9.2.2.2. Nested while loops
The example below was written to copy pictures that are made with a webcam to a web directory. Every five
minutes a picture is taken. Every hour, a new directory is created, holding the images for that hour. Every day,
a new directory is created containing 24 subdirectories. The script runs in the background.
#!/bin/bash
# This script copies files from my homedirectory into the webserver directory.
# (use scp and SSH keys for a remote directory)
# A new directory is created every hour.
PICSDIR=/home/carol/pics
WEBDIR=/var/www/carol/webcam
while true; do
DATE=`date +%Y%m%d`
HOUR=`date +%H`
mkdir $WEBDIR/"$DATE"
while [ $HOUR -ne "00" ]; do
DESTDIR=$WEBDIR/"$DATE"/"$HOUR"
mkdir "$DESTDIR"
mv $PICDIR/*.jpg "$DESTDIR"/
sleep 3600
HOUR=`date +%H`
done
done
Note the use of the true statement. This means: continue execution until we are forcibly interrupted (with kill
or Ctrl+C).
This small script can be used for simulation testing; it generates files:
#!/bin/bash
# This generates a file every 5 minutes
while true; do
Chapter 9. Repetitive tasks 110