+++
date = "2020-04-29T05:04:26+00:00"
publishdate = "2023-12-29T07:08:55+00:00"
title = "Tweaking the Bash Shell"
slug = "tweaking-the-bash-shell"
author = "Thedro"
tags = ["bash"]
type = "posts"
summary =  "The Bourne Again Shell is ubiquitous among many unix-like systems. Here's a few tweaks that are applied to my bash configuration for improved interactivity."
draft =  ""
syntax =  "1"
toc =  ""
updated =  "2020-05-27"
+++

{{< image source="/images/tweaking-the-bash-shell.png" title="Bourne-again shell" >}}
Bourne-Again Shell {{< /image >}}

The [Bourne Again](https://tiswww.case.edu/php/chet/bash/bashtop.html)
{{< sidenote mark="Shell" set="left" >}}[`fish`](https://fishshell.com/) and
[`zsh`](https://ohmyz.sh/) are popular alternative shells.{{< /sidenote>}} is
ubiquitous among many unix-like systems. Here's a few tweaks that are applied to
my `bash` configuration for {{< sidenote mark="improved" set="right" >}}My
preference is to not add too many tweaks (like aliases) to avoid building up bad
muscle memory.{{< /sidenote>}} interactivity.

## Conditional Prompt Colors

The color {{< sidenote mark="distinction" set="left" >}}This acts as a guide
when ascending and descending through shells.{{< /sidenote>}} in the prompt
gives a visual cue for the current environment. Green is indicative of a secure
shell connection (SSH), red of `root` privilege, blue of the standard user, and
white (an unmodified prompt) of a foreign system.

{{< image source="/images/bash-tweaks-color-prompts.gif" title="Prompt Colors in Bash" >}}
Prompt color changes based on the current context {{< /image >}}

This is achieved by short circuiting the `$PS1` (the primary
{{< sidenote mark="prompt" set="right" >}}My preferred `PS1` is not particularly
verbose.{{< /sidenote>}} variable) in `~/.bash_profile`.

```bash
PS1_USER='\[\e[0;34m\]\W\[\e[0m\] \[\e[0;34m\]\$\[\e[0m\] '
PS1_ROOT='\[\e[0;31m\]\W\[\e[0m\] \[\e[0;31m\]\$\[\e[0m\] '
PS1_SSHD='\[\e[0;32m\]\W\[\e[0m\] \[\e[0;32m\]\$\[\e[0m\] '

[ "$EUID" != 0 ] && export PS1="$PS1_USER";
[ "$EUID" = 0 ] && export PS1="$PS1_ROOT";
[ -n "$SSH_CLIENT" ] && [ "$EUID" != 0 ] && export PS1="$PS1_SSHD";
```

## Exit Codes

Often there is a need to know the return or exit status of the last command.
This is extremely useful in varied situations. The variable `$?` contains the
exit status of the last command.

{{< image source="/images/bash-tweaks-return-codes.gif" title="Prompt Return Codes" >}}
Prompt shows the exit status of the last command {{< /image >}}

In `~/.bash_profile`, the logic `$(E=$? && [ "$E" != 0 ] && echo "$E ")` is
prefixed to the `$PS1`. The exit status will be printed on a carriage return.

```bash
PS1_USER='$(E=$? && [ "$E" != 0 ] && echo "$E ")\[\e[0;34m\]\W\[\e[0m\] \[\e[0;34m\]\$\[\e[0m\] '
PS1_ROOT='$(E=$? && [ "$E" != 0 ] && echo "$E ")\[\e[0;31m\]\W\[\e[0m\] \[\e[0;31m\]\$\[\e[0m\] '
PS1_SSHD='$(E=$? && [ "$E" != 0 ] && echo "$E ")\[\e[0;32m\]\W\[\e[0m\] \[\e[0;32m\]\$\[\e[0m\] '

[ "$EUID" != 0 ] && export PS1="$PS1_USER";
[ "$EUID" = 0 ] && export PS1="$PS1_ROOT";
[ -n "$SSH_CLIENT" ] && [ "$EUID" != 0 ] && export PS1="$PS1_SSHD";
```

## Fuzzy Finder

The command line fuzzy finder [fzf](https://github.com/junegunn/fzf) has
[keybindings](https://github.com/junegunn/fzf#key-bindings-for-command-line) for
common operations in `bash` and `zsh`. This gives the
{{< sidenote mark="shell" set="right" >}}The terminal emulator in use is
`urxvt`. [Simple Terminal](https://st.suckless.org/) (`st`) is also rather
delightful and popular among the purists.{{< /sidenote>}} a more opinionated
reverse lookup (`CTRL+R`) workflow.

{{< image source="/images/bash-tweaks-fzf.gif" title="Command Line Fuzzy Finder" >}}
Command Line Fuzzy Finder {{< /image >}}

Source the fuzzy finder's keybindings in the `~/.bashrc` configuration. This
only works if the command `fzf` has been installed on the
{{< sidenote mark="system." set="left" >}}These paths are derived from Debian
and Arch based systems.{{< /sidenote>}}

```bash
[ -f '/usr/share/fzf/completion.bash' ] && . /usr/share/fzf/completion.bash
[ -f '/usr/share/fzf/key-bindings.bash' ] && . /usr/share/fzf/key-bindings.bash
[ -f '/usr/share/doc/fzf/examples/completion.bash' ] && . /usr/share/doc/fzf/examples/completion.bash
[ -f '/usr/share/doc/fzf/examples/key-bindings.bash' ] && . /usr/share/doc/fzf/examples/key-bindings.bash
```

## Vi Mode

Bash has a built in readline `vi` mode. This removes the tempting dependency on
the mouse for precise text manipulation. The prefixed `+` and `:`
{{< sidenote mark="symbols" set="right" >}}You can use anything you
want.{{< /sidenote>}} indicate `insert` and `normal` modes respectively.
Pressing `v` in normal mode invokes `vim` on the current command.

{{< image source="/images/bash-tweaks-vi-mode.gif" title="Vi Mode" >}} Vi Mode
{{< /image >}}

Use the `set` command in the `~/.inputrc`
{{< sidenote mark="file" set="right" >}}Create this file inside the user's home
directory.{{< /sidenote>}} to enable showing the `vi` mode prompt.

```bash
set show-mode-in-prompt on
set vi-ins-mode-string "+ "
set vi-cmd-mode-string ": "
```

Use the `set` command to enable `vi`
{{< sidenote mark="mode" set="left" >}}There is also an `emacs`
mode.{{< /sidenote>}} by adding the directive in `~/.bashrc`.

```bash
set -o vi;
```

## Readline Configuration

The shell's `readline` can be configured in the `~/.inputrc` file. Here's a few
other `readline` tweaks for a sane setup.

```bash
# Set colors on completion results.
set colored-stats on

# Ignore case when using tab completion.
set completion-ignore-case on

# Show completion results on the first tab press.
set show-all-if-ambiguous on

# Avoid inserting tab completions in the middle of a word.
set skip-completed-text on

# Up and down reverse search will consider the currently typed command.
"\e[A": history-search-backward
"\e[B": history-search-forward
```