Handy Bash Commands

Clear the Contents of a File

If you need to clear out everything in a file, use the truncate command.

truncate -s 0 filename.txt

As the name implies, you can also truncate only part of the file, or even extend it.

Stop a Script on Error

This is one of those weird, counter-intuitive bash footguns. By default, if a command in a script fails, the rest of the script continues execution anyway. To stop execution if a command fails, use set -e at the beginning of the script.

#!/bin/bash
set -e

# the rest of your script...

Suspend a Command or Shell

Commands or shells can be suspended, yielding control back to the parent shell until they are restarted with SIGCONT or the fg command, depending on the context.

Shells can be suspended with the suspend command. For instance, to drop out of a super-user shell for a moment.

user$ sudo su
root# # Do Something as su
root# suspend
bash: suspended (signal) sudo su
user$ # Back to original user
user$ fg
[1]+  Continued    sudo su 
root# # Back to su

Commands (and text editors!) can often be suspended using C-z. Try it with less.

user$ less my/file.txt
... Press C-z
[1]+  Stopped      less my/file.txt
user$ fg
... back to less

This functions like a stack. You can layer on suspended shells or commands, and fg pops off the top one.