199 lines
3.1 KiB
Markdown
199 lines
3.1 KiB
Markdown
---
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author: "Devoalda"
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authorEmoji: 🐺
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title: "Bash Cheatsheet"
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date: 2020-07-06T16:47:03+08:00
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description: Simple Bash Cheatsheet
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draft: false
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hideToc: false
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enableToc: true
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enableTocContent: true
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tocPosition: inner
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tocLevels: ["h1", "h2", "h3"]
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tags:
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- bash
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- linux
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- script
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- cheetsheet
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series:
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- Bash
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categories:
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- bash
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- script
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image: images/postImages/Bash_256x256.png
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---
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# Introduction
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This is a simple bash script cheatsheet.
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# Variables
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## Define variables
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```bash
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abc=123
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hello=321
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qwerty=asdf
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```
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### Assign output of command to variable
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``` bash
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music=$(mpc)
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```
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### Argument
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```bash
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word=$1
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```
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### Argument and default value
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``` bash
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words=${1-hello} # If variable not set or null, use default.
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FOO=${VARIABLE:=default} # If variable not set or null, set it to default.
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```
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{{< alert theme="info" dir="ltr" >}}
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Ensure no spaces between variable name and value
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{{< /alert >}}
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## View variable content
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```bash
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$ echo $abc
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# outputs: 123
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$ echo "$(echo "upg")"
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# outputs: upg
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$ echo '$(echo "upg")'
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# outputs: $(echo "upg")
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```
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# Loops
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## For loop
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``` bash
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for i in {1..5}
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do
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echo "Hello $i"
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done
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```
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### {START..END..INCREMENT}
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``` bash
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for i in {0..10..2}
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do
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echo "Hello $i"
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done
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```
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### Files
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``` bash
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for file in $HOME
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do
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echo $file
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done
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```
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## While loop
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``` bash
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while [ condition ]
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do
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echo "hello"
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done
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```
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### Infinite while loop
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``` bash
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while true
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do
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echo "hello"
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done
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```
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{{< alert theme="info" dir="ltr" >}}
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Hit CTRL-C to stop the loop
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{{< /alert >}}
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### Read File
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``` bash
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#!/usr/bin/env bash
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FILE=${1-hello.txt}
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while read line
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do
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# use $line variable to process line
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echo $line
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done < "$FILE"
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```
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# If Else Loop
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``` bash
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if [ condition ]; then
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echo 1
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elif [ condition2 ]; then
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echo 2
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else
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echo 3
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fi
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```
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# Conditions
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| Operator | Description |
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|-----------|--------------------------|
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| -eq | Equal |
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| -lt | Less than |
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| -le | Less than or equal to |
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| -gt | Greater than |
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| -ge | Greater than or equal to |
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| == | 2 Strings equal |
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| != | 2 Strings not equal |
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| ! | Statement is false |
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| -d | Directory is present |
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| -e | File is present |
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| -z "$1" * | Check for empty argument |
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{{< alert theme="info" dir="ltr" >}}
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\* Note the space between the operator and argument
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```bash
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[ -z "$1" ]
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```
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{{< /alert >}}
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## Condition Usage Examples
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``` bash
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if [[ "$1" == "bash" && "$2" = "shell" ]]; then
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echo "$1 $2"
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elif [ "$1" == "bash" ]; then
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echo "$1"
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elif [ -e "$HOME/hello.txt" ]
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echo "File Present"
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elif [ ! -d "$HOME/Documents" ]
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echo "Directory NOT Present"
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else
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echo Condition
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fi
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```
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# Case
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``` bash
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word=$1
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case "$word" in
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hello)
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echo hello
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;;
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bye)
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echo bye
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;;
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*)
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echo Universal
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;;
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esac
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```
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# Functions
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``` bash
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function fun(){
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echo fun
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}
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```
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{{< expand "Credits/References" >}}
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[stackoverflow1](https://stackoverflow.com/questions/6697753/difference-between-single-and-double-quotes-in-bash)
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[stackoverflow2](https://stackoverflow.com/questions/2013547/assigning-default-values-to-shell-variables-with-a-single-command-in-bash)
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{{< /expand >}}
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