Uses of the sed Quit Command (Unix Power Tools, 3rd Edition)

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34.22. Uses of the sed Quit Command

The quit command, q, causes sed to stop reading new input lines (and stop sending them to the output). Its syntax is:

[line-address]q

It can take only a single-line address. Once the line matching address (line-address) is reached, the script will be terminated.

For instance, the following one-liner uses the quit command to print the first ten lines from a file:

% sed '10q' myfile
   ...

sed prints each line until it gets to line 10 and quits.

The previous version is much more efficient than its functional equivalent:

-n Section 34.3

% sed -n '1,10p' myfile

(especially if myfile is a long file) because sed doesn't need to keep reading its input once the patterns in the script are satisfied.

One possible use of q is to quit a script after you've extracted what you want from a file. There is some inefficiency in continuing to scan through a large file after sed has found what it is looking for.

-- TOR


34.21. The sed Test Command		34.23. Dangers of the sed Quit Command