Exercise: Test Multiple Aspects

Test Multiple Aspects
In many situations you will want to test for multiples aspects of the file or directory.    There are also a number of ways that you can set up these multiple tests.  This example looks for a file that exists and is writable.

#!/bin/bash
file=/etc/yum.repos.d/rpmforge.repo
if [ -f $file  ] && [ -w $file ]
then
echo $file exists and is writable
else
echo  $file exists but it is not writable
fi

Exercise:
Create a script that tests for the existence of a file and determines if it is writeable.

As a regular user create a test directory and then create an empty file called log.  Notice this command does it all on one line separating commands with a semi-colon.
cd;mkdir test;cd test;touch log

Use the test builtin to verify how the script will work.  This is a simple process in starting to build a script.  The “-w” option is to see if the file is writeable and the “-f” option is to see if the file is a file (as opposed to a directory,link etc.).  The “echo $?” is showing the success of failure of the command.  So if the command is executed and you see “0″ that is success, any other number is failure.

[ -w log ];echo $?
0
[ -f log ];echo $?
0
You could have also done this:

test -w log;echo $?
0
test -f log;echo $?
0

Now you have the basics working from the command line, build it into a script.  The variable “chkfile” can be used to list any file you want down the road.    The test checks to see if the file is a file and if that command produces a “0″ (success) it executes the second command which checks to see if the file is writeable.  The if…then..else allows you to choose the output of your command.

#!/bin/bash
chkfile=log
if [ -f $chkfile ] && [ -w $chkfile ]
then
echo $chkfile exists and it is writeable
else
echo $chkfile exists but is not writeable
fi

Make the script executable.

chmod 755 test.sh

Execute teh script.
./test.sh

Tagged as: test