18.7.1 The if Control Command
The if command is used to check expressions. For example, the following code tests
whether the current user is Tux:
if test $USER = "tux"; then
echo "Hello Tux."
else
echo "You are not Tux."
fi
The test expression can be as complex or simple as possible. The following expression
checks if the le foo.txt exists:
if test -e /tmp/foo.txt ; then
echo "Found foo.txt"
fi
The test expression can also be abbreviated in angled brackets:
if [ -e /tmp/foo.txt ] ; then
echo "Found foo.txt"
fi
Find more useful expressions at http://www.cyberciti.biz/nixcraft/linux/docs/
uniqlinuxfeatures/lsst/ch03sec02.html.
18.7.2 Creating Loops With the For Command
The for loop allows you to execute commands to a list of entries. For example, the
following code prints some information about PNG les in the current directory:
for i in *.png; do
ls -l $i
done
18.8 For More Information
Important information about Bash is provided in the man pages man bash. More about
this topic can be found in the following list:
•
http://tldp.org/LDP/Bash-Beginners-Guide/html/index.html—Bash Guide for
Beginners
•
http://tldp.org/HOWTO/Bash-Prog-Intro-HOWTO.html—BASH Programming - In-
troduction HOW-TO
•
http://tldp.org/LDP/abs/html/index.html—Advanced Bash-Scripting Guide
•
http://www.grymoire.com/Unix/Sh.html—Sh - the Bourne Shell
236 Start-Up
