Shell

What I do

• Use shell commands effectively
• Write robust shell scripts
• Manage processes and jobs
• Handle I/O redirection and pipes
• Automate tasks
• Debug shell scripts

When to use me

When working in terminal, automating tasks, or writing shell scripts.

Shell Types

• bash: Bourne Again Shell, most popular
• zsh: Z Shell, Oh My Zsh, advanced features
• fish: Friendly Interactive Shell, user-friendly
• sh: POSIX shell, portable

Basic Commands

File Operations

ls -la          # List with details
cp -r           # Copy recursive
rm -rf          # Force remove
mkdir -p        # Create nested dirs
chmod           # Change permissions
chown           # Change owner

Text Processing

cat             # View file
grep            # Search pattern
sed             # Stream editor
awk             # Text processing
sort            # Sort lines
uniq            # Unique lines
head/tail       # First/last lines
wc              # Word count

System

ps              # Process status
top/htop        # Process monitor
kill            # Kill process
df              # Disk free
du              # Disk usage
free            # Memory

Scripting

Shebang

#!/bin/bash
#!/usr/bin/env bash

Variables

NAME="John"
echo $NAME
echo ${NAME}
# Arrays
arr=(one two three)
echo ${arr[0]}

Conditionals

if [ $name = "admin" ]; then
    echo "Hello admin"
elif [ $name = "guest" ]; then
    echo "Hello guest"
else
    echo "Hello stranger"
fi

Loops

# For loop
for f in *.txt; do
    echo "Processing $f"
done

# While loop
while read line; do
    echo "$line"
done < file.txt

Functions

greet() {
    local name=$1
    echo "Hello, $name"
}
greet "World"

Advanced Features

I/O Redirection

>   # Redirect stdout
2>  # Redirect stderr
&>  # Redirect both
>>  # Append
<   # Redirect stdin
|   # Pipe

Process Substitution

diff <(ls dir1) <(ls dir2)

Parameter Expansion

${var:-default}  # Default if unset
${var:=default}  # Set default
${var:?error}   # Error if unset
${var#pattern}  # Remove prefix
${var%pattern}  # Remove suffix
${var/old/new} # Replace

Globbing

*.txt       # All txt files
file?.txt   # file1.txt, file2.txt
[abc]*.txt  # Starting with a,b,c

Best Practices

• Use set -euo pipefail
• Quote variables
• Use [[ ]] over [ ]
• Add comments
• Use functions
• Check exit codes
• Use shellcheck
• Make scripts portable