bash

What it does

How to write it

bash [OPTION]... [-c COMMAND | SCRIPT [ARGUMENT]...]

Most used

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$ run as a normal user# run as root (or with sudo)

1. 1Run a script

   $bash backup.sh

   Works even without the x permission.

2. 2Check the syntax

   $bash -n backup.sh

   No output = no syntax error.

3. 3Trace a script

   $bash -x backup.sh 2>&1 | less

   Each command with filled-in values (lines start with +).

4. 4Run one command line

   $bash -c 'for i in 1 2 3; do echo $i; done'

   Useful with sudo, ssh and find -exec.

5. 5A clean shell for tests

   $bash --noprofile --norc

   Without your aliases and settings.

6. 6Start a login shell

   $bash -l

   Reads the profile files again (after changes).

7. 7Which shell am I using?

   $echo $SHELL; ps -p $$ -o comm=
   /bin/bash
   bash

   $SHELL is the login shell; ps shows the running one.

8. 8Version (for script features)

   $bash --version | head -1

   RHEL 10 has bash 5.2.

9. 9Run a script with sudo and a heredoc

   $sudo bash -s <<'EOF2'
   dnf -y upgrade
   systemctl restart httpd
   EOF2

   Several root commands in one go.

10. 10Find scripts with strict settings

    $grep -l 'set -euo pipefail' /usr/local/bin/*.sh

    Scripts that stop on errors.

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Files

/etc/profile, /etc/profile.d/

Login settings for all users.

/etc/bashrc

Interactive settings for all users.

~/.bash_profile, ~/.bashrc

Personal settings.

~/.bash_history

Command history.

Exit codes