Learning Linux Shell Scripting - Second Edition

Understanding sed

Whenever you use sed commands on a text file, sed reads the first line of the file and stores it in a temporary buffer called pattern space. sed processes this pattern space buffer as per commands given by the user. Then, it prints the output on screen. This line from the pattern space is then removed and the next line of the file is loaded in the pattern space. In this way, it processes all the lines one by one. This line-by-line processing is continued till the last line of the file. As the sed commands are processed in the temporary buffer or pattern space, the original line is not modified. Therefore, we say sed is a non-destructive buffer: