Bash One-Liners

Table of Contents

Empty a File #

If the file does not exist, it is created. If it does exist it is truncated to zero size.

# > file.txt

MacBook-Pro:tmp kavish$ cat file.txt
not empty
MacBook-Pro:tmp kavish$
MacBook-Pro:tmp kavish$ > file.txt
MacBook-Pro:tmp kavish$
MacBook-Pro:tmp kavish$ cat file.txt
MacBook-Pro:tmp kavish$
MacBook-Pro:tmp kavish$ ls -lh file.txt
-rw-r--r--  1 kavish  wheel     0B Apr 13 15:46 file.txt
MacBook-Pro:tmp kavish$

Copy a file quickly with brace expansion #

This is my favourite. To copy a file at /etc/ssh/sshd_config to /etc/ssh/sshd_config.bak, you’d run:

cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak

Unless you change into that directory, you’d just run:

cp sshd_config sshd_config.backup

You can use brace expansion instead {...}. The sytax is cp path{,extension}

MacBook-Pro:workshop kavish$ pwd
/tmp/workshop
MacBook-Pro:workshop kavish$
MacBook-Pro:workshop kavish$ ls /tmp/file.*
/tmp/file.txt
MacBook-Pro:workshop kavish$
MacBook-Pro:workshop kavish$ cp /tmp/file.txt{,.backup} # brace expansion
MacBook-Pro:workshop kavish$
MacBook-Pro:workshop kavish$ ls /tmp/file.*
/tmp/file.txt      /tmp/file.txt.backup 
MacBook-Pro:workshop kavish$

Create multiple files with brace expansion #

MacBook-Pro:workshop kavish$ echo {1..2}
1 2
MacBook-Pro:workshop kavish$ touch file{1..2}
MacBook-Pro:workshop kavish$
MacBook-Pro:workshop kavish$ ls
file1 file2

Prevent Overwriting of a file when redirecting output #

set -o noclobber

If you’re sure that you’ve to overwrite a file, you can override noclobber, by using >|:

ls -l >| file.txt

w >| logged_in_users.txt

Last word used #

Syntax: command !$.

MacBook-Pro:tmp kavish$ cat file.txt
hello world
MacBook-Pro:tmp kavish$
MacBook-Pro:tmp kavish$
MacBook-Pro:tmp kavish$ ls -l !$
ls -l file.txt
-rw-r--r--  1 kavish  wheel  12 Apr 14 08:48 file.txt
MacBook-Pro:tmp kavish$

Erase all shell history #

rm ~/.bash_history

Stop logging history for the current session #

unset HISTFILE

The HISTFILE variable points to the file where the shell history should be saved.