pure bash

A [WIP] collection of pure bash alternatives to external processes.

The goal of this repository is to document known and unknown methods of doing various tasks using only built-in bash features. Using the snippets from this guide can help to remove unneeded dependencies from your scripts and in most cases make them that little bit faster. I came across these tips and discovered a few while developing neofetch, pxltrm and some other smaller projects.

This repository is open to contribution. If you see something that is incorrectly described, buggy or outright wrong, open an issue or send a pull request. If you know a handy snippet that is not included in this list, send a pull request!

NOTE: Error handling (checking if a file exists, etc) is not included. These are meant to be snippets you can incorporate into your scripts and not full blown utilities.

Table of Contents

• File handling
  • Read a file to a string.
  • Read a file to an array (by line).
  • Get the first N lines of a file.
  • Get the last N lines of a file.
  • Get the number of lines in a file.
• Strings
  • Get the directory name of a file path.
  • Change a string to lowercase.
  • Change a string to uppercase.
  • Trim quotes from a string.
• Arrays
  • Reverse an array.
• Colors
  • Convert a hex color to RGB.
  • Convert an RGB color to hex.
• Miscellaneous
  • Getting the terminal size (in a script).
  • Get the current date using strftime.

File handling

Read a file to a string.

Alternative to the cat command.

file_data="$(<"file")"

Read a file to an array (by line).

Alternative to the cat command.

IFS=$'\n' read -d "" -ra file_data < "file"

Get the first N lines of a file.

Alternative to the head command.

NOTE: Requires bash 4+

head() {
    # Usage: head "n" "file"
    mapfile -tn "$1" line < "$2"
    printf '%s\n' "${line[@]}"
}

Get the last N lines of a file.

Alternative to the tail command.

NOTE: Requires bash 4+

tail() {
    # Usage: tail "n" "file"
    mapfile -tn 0 line < "$2"
    printf '%s\n' "${line[@]: -$1}"
}

Get the number of lines in a file.

Alternative to wc -l.

NOTE: Requires bash 4+

lines() {
    # Usage lines "file"
    mapfile -tn 0 lines < "$1"
    printf '%s\n' "${#lines[@]}"
}

Strings

Get the directory name of a file path.

Alternative to the dirname command.

dirname() {
    # Usage: dirname "path"
    printf '%s\n' "${1%/*}/"
}

Change a string to lowercase.

NOTE: Requires bash 4+

lower() {
    # Usage: lower "string"
    printf '%s\n' "${1,,}"
}

Change a string to uppercase.

NOTE: Requires bash 4+

upper() {
    # Usage: upper "string"
    printf '%s\n' "${1^^}"
}

Trim quotes from a string.

trim_quotes() {
    # Usage: trim_quotes "string"
    : "${1//\'}"
    printf "%s\\n" "${_//\"}"
}

Arrays

Reverse an array.

Enabling extdebug allows access to the BASH_ARGV array which stores the current function’s arguments in reverse.

reverse_array() {
    # Usage: reverse_array "array"
    #        reverse_array 1 2 3 4 5 6
    shopt -s extdebug
    f()(printf '%s ' "${BASH_ARGV[@]}"); f "$@"
    shopt -u extdebug

    printf '\n'
}

Colors

Convert a hex color to RGB.

hex_to_rgb() {
    # Usage: hex_to_rgb "#FFFFFF"
    ((r=16#${1:1:2}))
    ((g=16#${1:3:2}))
    ((b=16#${1:5:6}))

    printf '%s\n' "$r $g $b"
}

Convert an RGB color to hex.

rgb_to_hex() {
    # Usage: rgb_to_hex "r" "g" "b"
    printf '#%02x%02x%02x\n' "$1" "$2" "$3"
}

Miscellaneous

Getting the terminal size (in a script).

This is handy when writing scripts in pure bash and stty/tput can’t be called.

get_term_size() {
    # Usage: get_term_size

    # (:;:) is a micro sleep to ensure the variables are
    # exported immediately.
    shopt -s checkwinsize; (:;:)
    printf '%s\n' "$LINES $COLUMNS"
}

Get the current date using strftime.

Bash’s printf has a built-in method of getting the date which we can use in place of the date command in a lot of cases.

NOTE: Requires bash 4+

date() {
    # Usage: date "format"
    # See: 'man strftime' for format.
    printf "%($1)T\\n"
}