Learning Red Hat Linux, Third Edition

Shell Scripts

A shell script is simply a file that contains a set of commands to be run by the shell when invoked. By storing commands as a shell script, you make it easy to execute them again and again. As an example, consider a file named deleter, which contains the following lines:

echo -n Deleting the temporary files... 
rm -f *.tmp
echo Done.

The echo commands simply print text on the console. The -n option of the first echo command causes omission of the trailing newline character normally written by the echo command, so both echo commands write their text on a single line. The rm command removes all files having names ending in .tmp from the current working directory.

You can execute this script by issuing the sh command, as follows:

$ sh deleter

Tip

If you invoke the sh command without an argument specifying a script file, a new interactive shell is launched. To exit the new shell and return to your previous session, issue the exit command.

If the deleter file were in a directory other than the current working directory, you’d have to type an absolute path, for example:

$ sh /home/bill/deleter

You can make it a bit easier to execute the script by changing its access mode to include execute access. To do so, issue the following command:

$ chmod 555 deleter

This gives you, members of your group, and everyone else the ability to execute the file. To do so, simply type the absolute path of the file, for example:

$ /home/bill/deleter

If the file is in the current directory, you can ...