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?
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.
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.
Commented
Feb 5, 2015 at 20:39
true > filename
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.
You can use the user command : truncate
truncate -s 0 test.txt
("-s 0" to specify the size)
sudo echo > file just gives an error in such cases.
Commented
Aug 19, 2015 at 7:35
sudo bash -c '> filename' is how you use the Bash solutions with sudo.
Commented
Sep 14, 2015 at 19:03
: > 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.
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).
true (or its builtin alias :), although ultimately you don't need a command at all (see the accepted answer).
Commented
Jul 25, 2014 at 5:09
Below command should also work :
cat /dev/null > file.log
truncate isn't built-in in BSD like MacOS and bash isn't defult shell for some OS.
Commented
Mar 10, 2022 at 4:40
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
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.
maillog, even sudo > /var/log/maillog wouldn't clear it (permission denied)
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.
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
$ 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
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.
Commented
Jan 1, 2010 at 4:57
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.
It can be done using sed
sed -i d filename
awk but this will be too slow for large files.
Few alternatives:
ex +%d -scwq file.log
cp /dev/null file.log
vi +%d -escwq file.log
install -m600 /dev/null file.log
Also, if you have multiple files you can use the following:
for file in /path/to/file/*; do > $file; done
This is helpful for log files in the same directory.
If you have spaces in filenames, use:
for file in /path/to/file/*; do > "$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.)
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
echo "" > filename is the most reliable command across different shells running on Windows, MacOS, and Linux. So, if you deal with a heterogeneous environment, that might be the one you want to commit to memory.
Commented
Jun 25 at 21:45
With my permissions this is the only thing that worked:
touch temp.txt
sudo mv temp.txt original-file.txt
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).
In windows environment:
type nul >filename
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
