pure-bash-bible/README.md

<h1 align="center">pure bash</h1> <p align="center">A [WIP] collection of
pure bash alternatives to external processes.</p>

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](https://github.com/dylanaraps/neofetch),
[pxltrm](https://github.com/dylanaraps/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

<!-- vim-markdown-toc GFM -->

* [File handling](#file-handling)
    * [Get the first N lines of a file.](#get-the-first-n-lines-of-a-file)
    * [Get the last N lines of a file.](#get-the-last-n-lines-of-a-file)
    * [Get the number of lines in a file.](#get-the-number-of-lines-in-a-file)
* [Strings](#strings)
    * [Get the directory name of a file path.](#get-the-directory-name-of-a-file-path)
    * [Trim quotes from a string.](#trim-quotes-from-a-string)
* [Colors](#colors)
    * [Convert a hex color to RGB.](#convert-a-hex-color-to-rgb)
    * [Convert an RGB color to hex.](#convert-an-rgb-color-to-hex)
* [Miscellaneous](#miscellaneous)
    * [Getting the terminal size (*in a script*).](#getting-the-terminal-size-in-a-script)
    * [Get the current date using `strftime`.](#get-the-current-date-using-strftime)

<!-- vim-markdown-toc -->


## File handling

### Get the first N lines of a file.

Alternative to the `head` command.

**NOTE:** Requires `bash` 4+

```sh
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+

```sh
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+

```sh
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.

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

### Trim quotes from a string.

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

## Colors

### Convert a hex color to RGB.

```sh
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.

```sh
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.

```sh
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+

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