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Chapter 34 The sed Stream Editor |
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34.21 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
| Warning! | It can take only a single-line address.
Once the line matching address (line-address
) is reached, the script will be
terminated. |
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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 |
%
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(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. The getmac (43.20 ) script uses this technique.
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| 34.20 The sed Test Command | 
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34.22 Dangers of the sed Quit Command |
