What's this?

commandlinefu.com is the place to record those command-line gems that you return to again and again.

Delete that bloated snippets file you've been using and share your personal repository with the world. That way others can gain from your CLI wisdom and you from theirs too. All commands can be commented on, discussed and voted up or down.

If you have a new feature suggestion or find a bug, please get in touch via http://commandlinefu.uservoice.com/

Get involved!

You can sign-in using OpenID credentials, or register a traditional username and password.

First-time OpenID users will be automatically assigned a username which can be changed after signing in.

Universal configuration monitoring and system of record for IT.

Stay in the loop…

Follow the Tweets.

Every new command is wrapped in a tweet and posted to Twitter. Following the stream is a great way of staying abreast of the latest commands. For the more discerning, there are Twitter accounts for commands that get a minimum of 3 and 10 votes - that way only the great commands get tweeted.

» http://twitter.com/commandlinefu
» http://twitter.com/commandlinefu3
» http://twitter.com/commandlinefu10

Subscribe to the feeds.

Use your favourite RSS aggregator to stay in touch with the latest commands. There are feeds mirroring the 3 Twitter streams as well as for virtually every other subset (users, tags, functions,…):

Subscribe to the feed for:



May 19, 2015 - A Look At The New Commandlinefu
I've put together a short writeup on what kind of newness you can expect from the next iteration of clfu. Check it out here.
March 2, 2015 - New Management
I'm Jon, I'll be maintaining and improving clfu. Thanks to David for building such a great resource!

Top Tags





Empty a file

Terminal - Empty a file
> file.txt
2009-01-26 10:22:31
User: root
Empty a file

For when you want to flush all content from a file without removing it (hat-tip to Marc Kilgus).


There are 3 alternatives - vote for the best!

Terminal - Alternatives
truncate -s0 file
2009-10-24 16:31:03
User: pipping

The downside of output redirection is that you need permissions. So something like

> file

won't play nicely w/ sudo. You'd need to do something like

bash -c '> file'

instead, you could go w/

sudo truncate -s0 file
:> file
> file
> foobar.txt
truncate -s 0 file.txt
2012-07-30 06:50:30
User: quentin

Immediately make a file empty. This even works if the file is still being written to. Great for cleaning up huge log files!

Know a better way?

If you can do better, submit your command here.

What others think

Nice one! Some thing in *nix are so simple that you'd never imagine they exist :)

Comment by evad 357 weeks and 1 day ago

cat > file.txt followed by shift+ins allows you to insert your buffer content into file. ^d to finish the process

Comment by boombastic 356 weeks and 5 days ago

A similar useful trick which works with things like sudo and pfexec is "cp /dev/null file.txt"; that way you don't have to switch to another account to empty files which you do not own.

Comment by systemj 355 weeks and 5 days ago

To avert surprises, prepend ":" to perform specified redirections reliably:

: > foo

FWIW, the (built-in) null command ":" also expands arguments.

Comment by laburu 355 weeks and 5 days ago

laburu can you expand on the reliability issue you're referring to?

Comment by pixelbeat 355 weeks and 5 days ago

This is especially useful with large files that need to be cleared. I've run across a situation where the inodes ran out on the hd because people kept cat'ing /dev/null and redirecting it to file. That method kept the inodes locked.

Comment by leprasmurf 355 weeks and 4 days ago

It should be noted that this is a Bash-ism. This will hang in ZSH and throw an error to STDERR with BSD-CSH.

Comment by atoponce 352 weeks and 2 days ago

Excellent! Just what I was looking for

Comment by xenon87 351 weeks and 1 day ago

If you've done set -o noclobber the command will need to be:

>| file.txt

Comment by rtmhal 350 weeks ago

This is not just a is a Bash-ism it works fine on the korn shell too.. tested on ksh/HP-UX.

Comment by zlemini 336 weeks and 3 days ago

Perfect for clearing log files :)

Comment by okuehn 320 weeks and 4 days ago

Useful trick, thanks

One more question: if i need to not change the time of the emptied file?

How can i do?

thanks in advance

Comment by bugmenot 267 weeks and 6 days ago

That is very nice also becouse '>' command preserves the permissions

Comment by carlesso 255 weeks ago

Thanks! I used to make it longer with: echo "" > file.txt

Comment by ktonga 188 weeks and 4 days ago

The portability to zsh is because in zsh, the command invoked by "> file.txt" is the null command. When zsh is invoked in sh compatibility mode, the option sh_nullcmd will be automatically set, and the null cmd will be ":". If csh_nullcmd (csh compat mode triggers that), then the null cmd will cause an error.

Without a compatibility option, the _default_ null command in zsh is "cat", so "> file.txt" is equivalent to "cat > file.txt" and you'll need to type ctrl-D to get the same effect. Set the shell variable "NULLCMD" to another command to change it. So NULLCMD=: is equivalent to sh_nullcmd and will make the above work.

The suggestion from laburu to use ": > file.txt" is good and is the most portable solution, since its behaviour is guaranteed by POSIX rather than being a shell extension.

Comment by syscomet 184 weeks and 2 days ago

this does *not* work with zsh. It's much better to do ":>file.txt"

Comment by j_melis 170 weeks and 4 days ago

Your point of view

You must be signed in to comment.