Shell

A shell is a command-line interpreter that provides a command-line interface to interact with the many unix-like system.

Unix Shells

The following is a list of Unix shells that are POSIX compliant.

Bash is the GNU Projects shell. It is probably the most used and well known shell.
DASH is a small implementation of /bin/sh. It is significantly faster than Bash and it is recommende to set DASH to be the system shell.
Zsh is a shell designed to be interactive but also a powerful scripting language. It is often set to be the default user shell because of its user friendliness and a more features like the possibility for syntax highlighting and auto suggestions.

Usage

This section addresses various different functions by and actions that can be taken with shell commands.

For Loops

For loops can be especially useful when scripting. A function could be called on all the files in a directory. The following command shows the basic functionality and syntax of a for loop in a POSIX compliant shell. The command appends -1 to all files in the current working directory. It consists of the loop structure that cycles through all files *. and appends -1 using mv "$f" "${f}-1". The command aswell as the scope could be change to only cycle through specific filetypes or use another command.

for f in *
  do mv "$f" "${f}-1"
done

This command can also be shortened to a single line by using ; like the following shows.

for f in *; do mv "$f" "${f}-1"; done

Changing the Default User Shell

The default user shell can be changed with the following command. Change <path to shell> according to the shell to set. For ZSH this would be /bin/zsh.

chsh -s <path to shell>

Changing the System Shell /bin/sh

The system shell in some distributions is made up by a POSIX compliant mode of Bash. This can be slow at times and a shell like A shell like DASH would be much faster. This is a guide on how to persistently change the symlink /bin/sh from Bash to DASH. Run the following commands to install and link /bin/sh to the DASH shell.

yay -S dash
sudo ln -sfT /bin/dash /bin/sh

Afterwards create the file /usr/share/libalpm/hooks/bash-update.hook and fill it with the following text.

[Trigger]
Type = Package
Operation = Install
Operation = Upgrade
Target = bash

[Action]
Description = Re-pointing /bin/sh symlink to dash...
When = PostTransaction
Exec = /usr/bin/ln -sfT dash /usr/bin/sh
Depends = dash

Disown a Command

This section is based on a guide by baeldung. Disowning a command removes it from the current shell. Commands that are detached from a shell will not terminate upon its closure. A command can be disowned simply by appending & disown at the end of it. It will then provide the PID of the command that got disowned.

Silencing a Command

This section is based on a guide by baeldung. If the output of a command is unwanted it can be silenced. There are two parts that can be silenced independently. Non-error outputs (stdout) can be silenced by appending 1> /dev/null to the command. Due to the 1 being ommitable > /dev/null has the same effect. Error outputs (stderr) can be silenced by appending 2> /dev/null. The complete output of both stderr and stdout can be silenced by appending > /dev/null 2>&1 to the command. A shortened version of it not possible on all shells is &> /dev/null.

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