How to clear the contents of a file from the command line?

Question

I have a log file that has a bunch of stuff in it that I don't need anymore. I want to clear the contents.

I know how to print the contents to the screen:

cat file.log

I know how to edit the file, line-by-line:

nano file.log

But I don't want to delete each line one at a time. Is there a way to do it in one command without destroying the file to do it?

score 782 · Accepted Answer · edited Mar 23 '20 at 19:39

782

In bash, just

> filename

will do. This will leave you with an empty file filename.

PS: If you need sudo call, please consider to use truncate as answered here.

edited Mar 23 '20 at 19:39

Pablo A

1,545

answered Jan 01 '10 at 10:20

geek

10,136

118

This is probably the raddest command in the history of computing – blarg Dec 02 '13 at 16:34
8

On the contrary, @Arekkusandaa.Irujasukin; it works just fine in any version of Windows, so long as, as mentioned, you are using bash as your shell and not e. g. cmd.exe or PowerShell, neither of which are POSIXy enough to be expected to handle such things. – DopeGhoti Feb 05 '15 at 20:39
3

LInters complain, maybe more elegant is to true > filename – Pablo A Mar 23 '20 at 19:15
4

This is fancy and short, but it does have a couple of downsides. First it's not immediately obvious how to handle file permissions such as the need for sudo. Of course you can do it with sudo bash -c '> filename', but spawning a shell is (relatively) expensive. Second it can easily trip up interactive shells that will actually hang waiting for input. This is especially relevant if you want to copy bits of a script into a terminal and get the same results. For these reasons I suggest the truncate based answer is actually more robust. – Caleb Apr 19 '21 at 10:49
it does not work in zsh :-( – alper Sep 19 '23 at 18:08

score 246 · Answer 2 · answered Aug 20 '13 at 14:21

246

You can use the user command : truncate

truncate -s 0 test.txt

("-s 0" to specify the size)

http://www.commandlinefu.com/commands/view/12/empty-a-file

answered Aug 20 '13 at 14:21

nono

2,560

6

Best answer around, works when you're non-root (with sudo) — sudo echo > file just gives an error in such cases. – Dmitry Verkhoturov Aug 19 '15 at 07:35
17

@DmitryVerkhoturov: sudo bash -c '> filename' is how you use the Bash solutions with sudo. – Stuart P. Bentley Sep 14 '15 at 19:03
1

brew install truncate on os x with homebrew installed. – xaxxon Jul 04 '16 at 07:47
Works faster than echo – Miao1007 Nov 26 '18 at 06:30
This also works in a bash script, while > filename does not – Black Feb 23 '22 at 10:59
This is probably right tool if this is log file. just specifiy filesize limit, have it on cron and be done with it. – MD. Mohiuddin Ahmed Jun 12 '23 at 09:29

score 64 · Answer 3 · answered Jul 25 '14 at 22:51

64

: > file.log

Same as > filename in Bash, but works in more shells (credit). Redirects the output from the true builtin (which has no output) to filename.

answered Jul 25 '14 at 22:51

Stuart P. Bentley

1,081

20

Just do :> filename. Doesn't it look like a smiley? :> – minmaxavg Sep 14 '15 at 02:37
On a macOS, > filename freezes. But : > filename works. – shinokada Jul 28 '21 at 01:26

score 58 · Answer 4 · edited Jul 25 '14 at 07:15

58

You could do this:

echo -n "" > file.log

Using > to write the (null) input from echo -n to the file.

Using >> would append the null input to the file (effectively doing nothing but touching it).

edited Jul 25 '14 at 07:15

Stuart P. Bentley

1,081

answered Jan 01 '10 at 01:55

Thechickenmoo

689

1

This will leave a space in there. – dmckee --- ex-moderator kitten Jan 01 '10 at 01:58
I'm getting this: -bash: : command not found – Andrew Jan 01 '10 at 03:52
9

echo "" > will still give you a file with one character (a newline.) If you want to use echo, use "echo -n > file.log" to echo null. – Dave Forgac May 04 '12 at 19:47
It would be better to use a dedicated null-output command like true (or its builtin alias :), although ultimately you don't need a command at all (see the accepted answer). – Stuart P. Bentley Jul 25 '14 at 05:09
You might have some problems with sudo. – flapjack Jan 10 '19 at 02:44

score 17 · Answer 5 · answered May 10 '16 at 12:45

17

Below command should also work :

cat /dev/null > file.log

answered May 10 '16 at 12:45

paarth batra

271

this is what ive been using for many years with no error – MaXi32 Oct 13 '20 at 05:58
3

This one should be the best compatible answer because truncate isn't built-in in BSD like MacOS and bash isn't defult shell for some OS. – Weihang Jian Mar 10 '22 at 04:40

score 16 · Answer 6 · answered Dec 06 '12 at 20:48

ZSH

>! filename

ZSH will protect users from clobbering files using the io redirect operator >. If you use >! you can force the truncation of an existing file.

If you want ZSH to use Bash's redirection behavior, were there is no protection from file clobbering, then you need to set the clobber option for your shell.

More Info: http://zsh.sourceforge.net/Doc/Release/Redirection.html

score 13 · Answer 7 · edited Sep 13 '12 at 13:01

13

IF you want to do from inside a vim editor in command line, you can try this:

vim file.txt

Press Esc.

:1,$d

Press Enter.

You will find all lines deleted.

edited Sep 13 '12 at 13:01

slhck

228,104

answered Sep 12 '12 at 18:21

soum

139

This is the only thing that worked for my maillog, even sudo > /var/log/maillog wouldn't clear it (permission denied) – bobobobo Jan 16 '14 at 00:00
2

@bobobobo It doesn't work as sudo > /var/log/maillog means - run sudo, and put its output into the file. Obviously it puts output with current user permissions. Easier thing do sudo su to start root shell and then do > /var/log/maillog. – kan Oct 01 '14 at 10:13

score 7 · Answer 8 · answered Jan 01 '10 at 01:59

7

$ rm file.log; touch file.log

or

$ cat > file.log

followed by control-d.

or...or...or...

Ah. Here is a single command version:

$ dd if=/dev/null of=file.log

answered Jan 01 '10 at 01:59

dmckee --- ex-moderator kitten

7,877

2

Thechickenmoo's suggestion of echo "" > file.log is better than the cat option you show, in this situation, tho there are others where cat is more appropriate. both use the same shell redirection to do the heavy lifting. – quack quixote Jan 01 '10 at 04:57
2

You dont need to run the cat command. Just "> file.log" will do it. – camh Jan 01 '10 at 06:22
1

Removing the file will reset the creation date. – Matteo Jul 16 '13 at 12:40
1

Removing the file will cause programs watching that file to lose their pointer to it (i.e., it will have a new address in the filesystem).
Generally speaking, yes rm will accomplish the task of producing an empty file with the same name. But it's not going to be right for every use case.
– robert Dec 08 '17 at 23:21
+1 for Robert. The rm way is useless in case you have a process writing into the file, while you want this truncation look unnoticed for this process. – jmary Jan 11 '21 at 10:48

timeSmith · Answer 9 · 2015-04-15T13:03:45.020

5

If you need to sudo to superuser privilege to access the file then the accepted answer will not work. Using this does work:

truncate -s0 file

or explicitly with sudo:

sudo truncate -s0 file

More info here http://www.commandlinefu.com/commands/view/12/empty-a-file

edited Apr 15 '15 at 13:03

answered Jan 30 '15 at 19:11

timeSmith

320

score 3 · Answer 10 · answered May 26 '20 at 17:14

3

It can be done using sed

sed -i d filename

answered May 26 '20 at 17:14

apena

171

+1. and you can do also with awk but this will be too slow for large files. – Cuauhtli Jun 14 '20 at 20:41
@Cuauhtli, why would it be slow? – CervEd Jun 17 '21 at 18:06

score 2 · Answer 11 · answered Jun 22 '16 at 16:35

2

Also, if you have multiple files you can use the following:

for file in /path/to/file/*; do > $file; done

This is helpful for log files in the same directory.

answered Jun 22 '16 at 16:35

DomainsFeatured

219

score 2 · Answer 12 · answered Mar 15 '18 at 09:36

2

If you have spaces in filenames, use:

for file in /path/to/file/*; do > "$file"; done

(I could not to include it in comments to previous answer because I don't have 50 reputation. Sometimes limitations are contra productive.)

answered Mar 15 '18 at 09:36

d491049

21

score 2 · Answer 13 · answered Oct 25 '15 at 22:27

2

Few alternatives:

ex +%d -scwq file.log
cp /dev/null file.log
vi +%d -escwq file.log
install -m600 /dev/null file.log

answered Oct 25 '15 at 22:27

kenorb

25,417

score 1 · Answer 14 · edited May 26 '20 at 17:32

1

There are multiple ways to clear the file as listed below:

echo "" > filename
cat /dev/null > filename

Below examples are mostly used in shell scripting

just# > filename
: > filename

edited May 26 '20 at 17:32

Io-oI

8,193

answered May 26 '20 at 15:57

sudhams reddy

11

score 1 · Answer 15 · answered Mar 04 '14 at 00:10

1

With my permissions this is the only thing that worked:

touch temp.txt
sudo mv temp.txt original-file.txt

answered Mar 04 '14 at 00:10

Morgan

11

score 0 · Answer 16 · answered Sep 17 '20 at 08:02

0

In windows environment:

type nul >filename

answered Sep 17 '20 at 08:02

Wasif

8,474

score 0 · Answer 17 · edited Jun 22 '22 at 11:22

0

cat filename
cp filename filename.bak
cat /dev/null > test

This will empty the original file and but you can still access the backup if you need the old contents of the file

edited Jun 22 '22 at 11:22

MMM

2,778

answered Mar 17 '21 at 13:37

Narasimha Reddy

11

Welcome to Super User! Before answering an old question having an accepted answer (look for green ✓) as well as other answers ensure your answer adds something new or is otherwise helpful in relation to them. Here is a guide on [answer]. There is also [tour] for the site tour, and [help] for the help center. – help-info.de Mar 17 '21 at 16:59

score 0 · Answer 18 · answered Jan 01 '10 at 03:14

0

One line at a time?

Try vi(m), the lovely text editor that can do anything. In this case, navigate to a line, press d (for delete), and d again (for line).

answered Jan 01 '10 at 03:14

Phoshi

23,383

5

If you want to get rid of the whole file in vim, with the cursor at the top of the document, typing d G (that's d, then shift-G) will delete the entire file (d for delete, G for end of the file). I prefer your method, though (it gives me more time to think about whether or not I REALLY want to trash the file). – Babu Jan 01 '10 at 04:19
@Babu gg moves to the top so the entire sequence could be ggdG. – Bob Mar 04 '14 at 00:22

How to clear the contents of a file from the command line?

18 Answers18