Mastering Linux Shell Scripting - Second Edition

The substitute command

We have seen the p command for printing the pattern space. The p is actually a flag for the substitute command s.

The substitute command is written like this:

$ sed s/pattern/replacement/flags  

There are three common flags used with the substitute command:

• p: Print the original content
• g: Global replacement for all occurrences
• w: Filename: send results to a file

We will now look at the substitute command or s. With this command, we can replace one string with another. Again, by default, we send the output to the STDOUT and do not edit the file.

To replace the default shell of the user pi, we can use the following command:

sed -n ' /^pi/ s/bash/sh/p ' /etc/passwd  

We continue the earlier instance using the p command ...