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Here's a simple one. How do I truncate an existing file in linux? That is, how do I empty the contents of the file but keep the file. I can always delete the file then touch it but I was wondering if there's a single command that'll get the job done.

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up vote 11 down vote accepted

>output-file -- shortest possible version.

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accepted for shortness - btw what does the extra colon do in :>output-file ? – pygorex1 Dec 2 '09 at 21:06
No idea; probably best to ask mezgani since he was the one who suggested it. – womble Dec 2 '09 at 21:26
colon's a noop – Xepoch Dec 2 '09 at 21:29
This is the only correct answer. – Dennis Williamson Dec 2 '09 at 21:42
@Xepoch: Thanks; I couldn't find it mentioned in bash(1), it's too common a character. I suspected it was something like that, though. – womble Dec 2 '09 at 22:06

This solution is more efficient than cat, because it doesn't create a subprocess (in addition to the shell process):

true >output-file
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You may do easy :)


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This is short and it works in all major shells I use (bash, dash, zsh, pdksh, tcsh). – pts Dec 2 '09 at 22:31
yep, i think that not work on ksh – mezgani Dec 2 '09 at 23:03

I'm sure a harder-core *nix person will have a better idea, but I've always done:

cat /dev/null > output-file

To truncate files.

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echo -n > YOURFILE
will remove file contents and keep the file, structure and permission intact.

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