395 lines
8.4 KiB
Markdown
395 lines
8.4 KiB
Markdown
# pure sh bible
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A collection of pure POSIX `sh` alternatives to external processes
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## Table of Contents
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<!-- vim-markdown-toc GFM -->
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* [STRINGS](#strings)
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* [Strip pattern from start of string](#strip-pattern-from-start-of-string)
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* [Strip pattern from end of string](#strip-pattern-from-end-of-string)
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* [Trim all white-space from string and truncate spaces](#trim-all-white-space-from-string-and-truncate-spaces)
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* [Check if string contains a sub-string](#check-if-string-contains-a-sub-string)
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* [Check if string starts with sub-string](#check-if-string-starts-with-sub-string)
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* [Check if string ends with sub-string](#check-if-string-ends-with-sub-string)
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* [FILES](#files)
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* [Get the first N lines of a file](#get-the-first-n-lines-of-a-file)
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* [Get the number of lines in a file](#get-the-number-of-lines-in-a-file)
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* [Count files or directories in directory](#count-files-or-directories-in-directory)
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* [Create an empty file](#create-an-empty-file)
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* [FILE PATHS](#file-paths)
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* [Get the directory name of a file path](#get-the-directory-name-of-a-file-path)
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* [Get the base-name of a file path](#get-the-base-name-of-a-file-path)
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* [ESCAPE SEQUENCES](#escape-sequences)
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* [Text Colors](#text-colors)
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* [Text Attributes](#text-attributes)
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* [Cursor Movement](#cursor-movement)
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* [Erasing Text](#erasing-text)
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* [PARAMETER EXPANSION](#parameter-expansion)
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* [Replacement](#replacement)
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* [Length](#length)
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* [Default Value](#default-value)
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<!-- vim-markdown-toc -->
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# STRINGS
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## Strip pattern from start of string
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**Example Function:**
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```sh
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lstrip() {
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# Usage: lstrip "string" "pattern"
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printf '%s\n' "${1##$2}"
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}
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```
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**Example Usage:**
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```shell
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$ lstrip "The Quick Brown Fox" "The "
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Quick Brown Fox
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```
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## Strip pattern from end of string
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**Example Function:**
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```sh
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rstrip() {
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# Usage: rstrip "string" "pattern"
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printf '%s\n' "${1%%$2}"
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}
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```
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**Example Usage:**
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```shell
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$ rstrip "The Quick Brown Fox" " Fox"
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The Quick Brown
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```
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## Trim all white-space from string and truncate spaces
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This is an alternative to `sed`, `awk`, `perl` and other tools. The
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function below works by abusing word splitting to create a new string
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without leading/trailing white-space and with truncated spaces.
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**Example Function:**
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```sh
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# shellcheck disable=SC2086,SC2048
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trim_all() {
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# Usage: trim_all " example string "
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set -f
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set -- $*
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printf '%s\n' "$*"
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set +f
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}
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```
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**Example Usage:**
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```shell
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$ trim_all " Hello, World "
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Hello, World
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$ name=" John Black is my name. "
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$ trim_all "$name"
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John Black is my name.
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```
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## Check if string contains a sub-string
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**Using a case statement:**
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```shell
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case $var in
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*sub_string*)
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# Do stuff
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;;
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*sub_string2*)
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# Do more stuff
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;;
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*)
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# Else
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;;
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esac
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```
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## Check if string starts with sub-string
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**Using a case statement:**
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```shell
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case $var in
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sub_string*)
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# Do stuff
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;;
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sub_string2*)
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# Do more stuff
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;;
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*)
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# Else
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;;
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esac
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```
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## Check if string ends with sub-string
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**Using a case statement:**
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```shell
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case $var in
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*sub_string)
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# Do stuff
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;;
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*sub_string2)
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# Do more stuff
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;;
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*)
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# Else
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;;
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esac
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```
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# FILES
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## Get the first N lines of a file
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Alternative to the `head` command.
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**Example Function:**
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```sh
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head() {
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# Usage: head "n" "file"
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while read -r line; do
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[ "$i" = "$1" ] && break
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printf '%s\n' "$line"
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i=$((i+1))
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done < "$2"
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}
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```
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**Example Usage:**
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```shell
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$ head 2 ~/.bashrc
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# Prompt
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PS1='➜ '
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$ head 1 ~/.bashrc
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# Prompt
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```
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## Get the number of lines in a file
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Alternative to `wc -l`.
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**Example Function:**
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```sh
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lines() {
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# Usage: lines "file"
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while read -r _; do
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lines=$((lines+1))
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done < "$1"
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printf '%s\n' "$lines"
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}
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```
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**Example Usage:**
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```shell
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$ lines ~/.bashrc
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48
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```
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## Count files or directories in directory
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This works by passing the output of the glob to the function and then counting the number of arguments.
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**Example Function:**
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```sh
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count() {
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# Usage: count /path/to/dir/*
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# count /path/to/dir/*/
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printf '%s\n' "$#"
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}
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```
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**Example Usage:**
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```shell
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# Count all files in dir.
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$ count ~/Downloads/*
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232
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# Count all dirs in dir.
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$ count ~/Downloads/*/
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45
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# Count all jpg files in dir.
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$ count ~/Pictures/*.jpg
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64
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```
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## Create an empty file
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Alternative to `touch`.
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```shell
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:>file
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# OR (shellcheck warns for this)
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>file
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```
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# FILE PATHS
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## Get the directory name of a file path
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Alternative to the `dirname` command.
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**Example Function:**
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```sh
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dirname() {
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# Usage: dirname "path"
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printf '%s\n' "${1%/*}/"
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}
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```
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**Example Usage:**
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```shell
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$ dirname ~/Pictures/Wallpapers/1.jpg
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/home/black/Pictures/Wallpapers/
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$ dirname ~/Pictures/Downloads/
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/home/black/Pictures/
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```
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## Get the base-name of a file path
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Alternative to the `basename` command.
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**Example Function:**
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```sh
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basename() {
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# Usage: basename "path"
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path=${1%/}
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printf '%s\n' "${path##*/}"
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}
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```
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**Example Usage:**
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```shell
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$ basename ~/Pictures/Wallpapers/1.jpg
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1.jpg
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$ basename ~/Pictures/Downloads/
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Downloads
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```
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# ESCAPE SEQUENCES
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Contrary to popular belief, there is no issue in utilizing raw escape sequences. Using `tput` abstracts the same ANSI sequences as if printed manually. Worse still, `tput` is not actually portable. There are a number of `tput` variants each with different commands and syntaxes (*try `tput setaf 3` on a FreeBSD system*). Raw sequences are fine.
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## Text Colors
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**NOTE:** Sequences requiring RGB values only work in True-Color Terminal Emulators.
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| Sequence | What does it do? | Value |
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| -------- | ---------------- | ----- |
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| `\e[38;5;<NUM>m` | Set text foreground color. | `0-255`
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| `\e[48;5;<NUM>m` | Set text background color. | `0-255`
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| `\e[38;2;<R>;<G>;<B>m` | Set text foreground color to RGB color. | `R`, `G`, `B`
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| `\e[48;2;<R>;<G>;<B>m` | Set text background color to RGB color. | `R`, `G`, `B`
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## Text Attributes
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| Sequence | What does it do? |
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| -------- | ---------------- |
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| `\e[m` | Reset text formatting and colors.
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| `\e[1m` | Bold text. |
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| `\e[2m` | Faint text. |
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| `\e[3m` | Italic text. |
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| `\e[4m` | Underline text. |
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| `\e[5m` | Slow blink. |
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| `\e[7m` | Swap foreground and background colors. |
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## Cursor Movement
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| Sequence | What does it do? | Value |
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| -------- | ---------------- | ----- |
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| `\e[<LINE>;<COLUMN>H` | Move cursor to absolute position. | `line`, `column`
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| `\e[H` | Move cursor to home position (`0,0`). |
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| `\e[<NUM>A` | Move cursor up N lines. | `num`
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| `\e[<NUM>B` | Move cursor down N lines. | `num`
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| `\e[<NUM>C` | Move cursor right N columns. | `num`
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| `\e[<NUM>D` | Move cursor left N columns. | `num`
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| `\e[s` | Save cursor position. |
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| `\e[u` | Restore cursor position. |
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## Erasing Text
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| Sequence | What does it do? |
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| -------- | ---------------- |
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| `\e[K` | Erase from cursor position to end of line.
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| `\e[1K` | Erase from cursor position to start of line.
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| `\e[2K` | Erase the entire current line.
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| `\e[J` | Erase from the current line to the bottom of the screen.
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| `\e[1J` | Erase from the current line to the top of the screen.
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| `\e[2J` | Clear the screen.
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| `\e[2J\e[H` | Clear the screen and move cursor to `0,0`.
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# PARAMETER EXPANSION
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## Replacement
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${VAR#PATTERN}` | Remove shortest match of pattern from start of string. |
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| `${VAR##PATTERN}` | Remove longest match of pattern from start of string. |
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| `${VAR%PATTERN}` | Remove shortest match of pattern from end of string. |
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| `${VAR%%PATTERN}` | Remove longest match of pattern from end of string. |
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## Length
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${#VAR}` | Length of var in characters.
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## Default Value
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| Parameter | What does it do? |
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| --------- | ---------------- |
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| `${VAR:-STRING}` | If `VAR` is empty or unset, use `STRING` as its value.
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| `${VAR-STRING}` | If `VAR` is unset, use `STRING` as its value.
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| `${VAR:=STRING}` | If `VAR` is empty or unset, set the value of `VAR` to `STRING`.
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| `${VAR=STRING}` | If `VAR` is unset, set the value of `VAR` to `STRING`.
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| `${VAR:+STRING}` | If `VAR` is not empty, use `STRING` as its value.
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| `${VAR+STRING}` | If `VAR` is set, use `STRING` as its value.
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| `${VAR:?STRING}` | Display an error if empty or unset.
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| `${VAR?STRING}` | Display an error if unset.
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