Shell

A program that interprets user commands.

POSIX shell:

#todo https://en.wikipedia.org/wiki/Shebang_(Unix)

✏️ Note
In most shells && and || have the same precedence.

💡 Hint
Add & at the end of a command to run it in the background.

Best practices

Write POSIX shell
Use set -euf: exit on first error, disallow unknown variables, disable globing
Use cd "$(dirname "$0")" to run the script from its directory
Use = for string comparisons, -eq for numeric comparisons
Always lint scripts with ShellCheck

More: https://github.com/SixArm/unix-shell-script-tactics

Glob patterns

?: any single character
*: any number of characters
**: any number of characters including /

Sourcing vs Executing

Sourcing a script (. script.sh) will run its commands in the current shell process. Changes to the environment are visible in the current shell.

Executing a script (./script.sh) will run its commands in a new shell process. Changes to the environment are not visible in the current shell and lost when the script is finished.