bash

Unix shell and command language interpreter

TLDR

Run script

$ bash [script.sh]

Execute command

$ bash -c ["echo hello"]

Interactive login shell

$ bash -l

Read from stdin

$ echo "ls -la" | bash

Debug script

$ bash -x [script.sh]

Check syntax only

$ bash -n [script.sh]

SYNOPSIS

bash [options] [file] [arguments]

bash (Bourne Again SHell) is a Unix shell and command language interpreter. It's the default shell on most Linux distributions and macOS, providing command execution, scripting, job control, and extensive programming features.Bash is backward-compatible with the original Bourne shell (sh) while adding numerous improvements and modern features.

PARAMETERS

-c string

Execute command from string

-l, --login

Login shell (sources profile files)

-i

Interactive mode

-x

Print commands before execution (debug mode)

-n

Syntax check only (no execution)

-e

Exit on first error

-u

Error on undefined variables

-v

Verbose mode (print input lines)

--noprofile

Don't read profile files

--norc

Don't read ~/.bashrc

--posix

Behave according to POSIX standard

-r, --restricted

Start a restricted shell

--version

Display bash version

CONFIGURATION

~/.bashrc

Per-user configuration for interactive non-login shells. Aliases, functions, prompt customization.

~/.bash_profile

Per-user configuration for login shells. Typically sources ~/.bashrc.

~/.bash_logout

Executed when a login shell exits.

/etc/bash.bashrc

System-wide configuration for interactive shells.

/etc/profile

System-wide configuration for login shells.

FEATURES

- Command history (readline)- Tab completion- Job control (fg, bg, jobs)- Arithmetic evaluation- Arrays and associative arrays- Functions- Pattern matching and globbing- Process substitution- Here documents- Conditional execution- Loops and flow control

STARTUP FILES

Login shell

/etc/profile, ~/.bashprofile, ~/.bashlogin, ~/.profile

Interactive non-login

~/.bashrc

Non-interactive

$BASH_ENV

SPECIAL VARIABLES

$0 - Script name$1, $2, ... - Positional parameters$@ - All parameters$# - Parameter count$? - Exit status of last command$$ - Process ID$! - PID of last background job

INSTALL

sudo apt install bash

sudo dnf install bash

sudo pacman -S bash

sudo apk add bash

sudo zypper install bash

brew install bash

nix profile install nixpkgs#bash

CAVEATS

Bash-specific features not portable to POSIX sh. Scripts should use `#!/bin/bash` not `#!/bin/sh`. Unquoted variables can cause word splitting. Use `shellcheck` to validate scripts.

HISTORY

Bash was created by Brian Fox for the GNU Project in 1989 as a free replacement for the Bourne shell, first released as version 0.99. Version 5.0 was released in 2019.