Empty a file

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

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

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.

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

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

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

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.

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

Excellent! Just what I was looking for

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

>| file.txt

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

Perfect for clearing log files :)

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

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

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

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.

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