No Clobber

Ever unintentionally clobbered a file when redirecting some output to it?

$ cat some_file
foo bar

# Unintentionally overwrite 'some_file'
$ echo "potato" > some_file

$ cat some_file
potato

This can happen whenever the output file already exists. Or when you accidentally write to the file with > instead of appending to it using >>.

Most Linux shells actually have an option to prevent you from unintentionally overwriting files. It is generally called “no clobber” and you can enable it as follows:

# On Bash ~/.bashrc
set -o noclobber

# On Zsh ~/.zshrc
setopt NO_CLOBBER

This will make sure that the filename does not exist before trying to redirect data into it:

$ cat some_file
foo bar

# Unintentionally overwrite 'some_file'
$ echo "potato" > some_file
zsh: file exists: some_file

# 'some_file' remains untouched
$ cat some_file
foo bar

But what if we intentionally want to overwrite a file? In that case, we can tell bash to ignore the clobber by using >| instead:

$ echo "potato" >| some_file

$ cat some_file
potato