Linux System Administration

Useful Elements for bash Scripts

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Troubleshooting a Simple Script

Let’s perform some surgery on a script that is supposed to delete its argument (a file

or a directory) but has a few problems:

admin@server1:~$ cat delete

#!/bin/bash

if rm $1

then

echo file $1 deleted

else

if rmdir $1

then

echo directory $1 deleted

fi

fi

The script is intended to delete the file passed as an argument using rm, and to print

a message if it succeeds. If rm fails, the script assumes the argument refers to a direc-

tory and tries rmdir instead.

Here are some results:

admin@server1:~$ ./delete hello2

file hello2 deleted

admin@server1:~$ ./delete hello2

rm: cannot remove `hello2': No such file or directory

rmdir: `hello2': No such file or directory

admin@server1:~$ mkdir hello3

admin@server1:~$ ./delete hello3

rm: cannot remove `hello3': Is a directory

directory hello3 deleted

admin@server1:~

Using these error messages, let’s try to fix the script. First, we’ll use I/O redirection

to save results to log and error files, which we can review in our copious free time.

Next, we’ll catch the return value of the rm command to generate a success or fail-

ure message. We’ll also capture the current date and time to include in the output

log:

admin@server1:~$ cat removefiles

#!/bin/bash

# removefiles deletes either files or directories

echo "$0 ran at" $(date) >> delete.log

if rm $1 2>> delete-err.log

then

echo "deleted file $1" >> delete.log ...