bash.md

Bash is a powerful shell language for automating tasks on Unix-like systems. Below, we cover essential topics including permissions, configuration files, variables, conditionals, loops, aliases, and practical examples.

File Permissions

To execute a script, you need to add executable permissions to it. Use the following command for a file named script.sh:

chmod +x script.sh

The script file should start with the shebang line to specify the interpreter:

#!/bin/bash

PATH Configuration

To ensure that scripts in ~/bin/ are available, add this directory to your PATH. On Linux-style shells, modify ~/.bashrc, and on macOS (Catalina and later, which uses Zsh by default), modify ~/.zshrc.

# Edit the configuration file
nano ~/.zshrc

# Add the following line to the end of the file
export PATH=~/bin:$PATH

# Reload the configuration
source ~/.zshrc

Simple Commands

Output Text

echo "Hello World!"

Using Variables

Variables are defined without a $ and accessed with a $.

greeting="Hello"
echo $greeting

Conditionals

Use conditionals to make decisions in scripts.

if [ $index -lt 5 ]
then
  echo $index
else
  echo 5
fi

Comparison operators:

• Equal: -eq

• Not equal: -ne

• Less than: -lt

• Greater than: -gt

• Null check: -z

String comparison:

• Equal: ==

• Not equal: !=

Loops

For Loop

for word in $paragraph
do
  echo $word
done

While Loop

while [ $index -lt 5 ]
do
  echo $index
  index=$((index + 1))
done

Until Loop

until [ $index -eq 5 ]
do
  echo $index
  index=$((index + 1))
done

Inputs

Read input from the user and use it in your script.

read number
echo "You guessed $number"

Aliases

Aliases are shortcuts for commands. Define them in your configuration file.

alias saycolors='./saycolors.sh'
alias saycolors='./saycolors.sh "green"'