Shell Scripting for Developer Productivity

#!/bin/bash
# hello.sh — A simple greeting script

echo "Hello, World!"

chmod +x hello.sh
./hello.sh

#!/bin/bash

# Defining variables (no spaces around =)
name="Alice"
greeting="Hello"

# Using variables with $
echo "$greeting, $name!"

# Command substitution
current_date=$(date)
echo "Today is: $current_date"

# Arithmetic
count=$((5 + 3))
echo "Count: $count"

# Use uppercase for environment variables
export PROJECT_DIR="$HOME/projects/myapp"

# Use quotes to handle spaces
filename="my file.txt"
cat "$filename"  # Correct
cat $filename    # Wrong — splits on space

# Default values
echo "${name:-World}"  # Uses "World" if $name is unset

# Read-only variables
readonly VERSION="1.0.0"

#!/bin/bash

# if/elif/else
file="test.txt"

if [ -f "$file" ]; then
  echo "$file exists"
elif [ -d "$file" ]; then
  echo "$file is a directory"
else
  echo "$file does not exist"
fi

# Numeric comparison
count=42
if [ "$count" -gt 10 ]; then
  echo "Count is greater than 10"
fi

# String comparison
name="Alice"
if [ "$name" = "Alice" ]; then
  echo "Hello, Alice!"
fi

#!/bin/bash

# Loop over files
for file in *.txt; do
  echo "Processing $file"
  wc -l "$file"
done

# Loop over a range
for i in {1..5}; do
  echo "Iteration $i"
done

# Loop over command output
for user in $(cat /etc/passwd | cut -d: -f1); do
  echo "User: $user"
done

#!/bin/bash

# Read file line by line
while IFS= read -r line; do
  echo "Line: $line"
done < input.txt

# Countdown
count=5
while [ "$count" -gt 0 ]; do
  echo "$count..."
  count=$((count - 1))
  sleep 1
done
echo "Go!"

#!/bin/bash

# Define a function
greet() {
  local name="$1"
  echo "Hello, $name!"
}

# Function with return value
is_even() {
  local num=$1
  if [ $((num % 2)) -eq 0 ]; then
    return 0  # Success
  else
    return 1  # Failure
  fi
}

# Call functions
greet "Alice"

if is_even 42; then
  echo "42 is even"
fi

#!/bin/bash
set -e  # Exit on any error
set -u  # Exit on undefined variable
set -o pipefail  # Fail if any command in a pipe fails

# Or combine: set -euo pipefail

# Manual error checking
if ! mkdir -p "$OUTPUT_DIR"; then
  echo "Error: Could not create directory $OUTPUT_DIR" >&2
  exit 1
fi

# Trap errors
cleanup() {
  echo "Cleaning up..."
  rm -rf "$TEMP_DIR"
}
trap cleanup EXIT

TEMP_DIR=$(mktemp -d)
# ... do work ...
# cleanup runs automatically on exit

#!/bin/bash

usage() {
  echo "Usage: $0 -n <name> -o <output> [-v]"
  echo "  -n    Name (required)"
  echo "  -o    Output directory (required)"
  echo "  -v    Verbose mode"
  exit 1
}

verbose=false

while getopts "n:o:v" opt; do
  case $opt in
    n) name="$OPTARG" ;;
    o) output="$OPTARG" ;;
    v) verbose=true ;;
    *) usage ;;
  esac
done

if [ -z "${name:-}" ] || [ -z "${output:-}" ]; then
  usage
fi

if [ "$verbose" = true ]; then
  echo "Name: $name"
  echo "Output: $output"
fi

#!/bin/bash
# scaffold.sh — Create a new project structure

set -euo pipefail

PROJECT_NAME="${1:-my-project}"
PROJECT_DIR="$HOME/projects/$PROJECT_NAME"

create_project() {
  local name="$1"
  local dir="$2"

  echo "Creating project: $name"

  # Create directory structure
  mkdir -p "$dir"/{src,test,docs,scripts}
  mkdir -p "$dir/src"/{components,utils,styles}

  # Create files
  cat > "$dir/README.md" << EOF
# $name

Project description here.
EOF

  cat > "$dir/.gitignore" << EOF
node_modules/
dist/
.env
*.log
EOF

  cat > "$dir/package.json" << EOF
{
  "name": "$name",
  "version": "1.0.0",
  "scripts": {
    "dev": "vite",
    "build": "vite build",
    "test": "vitest"
  }
}
EOF

  # Initialize git
  cd "$dir"
  git init
  git add .
  git commit -m "Initial commit: scaffold $name"

  echo "Project created at: $dir"
}

if [ -d "$PROJECT_DIR" ]; then
  echo "Error: Directory $PROJECT_DIR already exists" >&2
  exit 1
fi

create_project "$PROJECT_NAME" "$PROJECT_DIR"

# Dry run (show commands without executing)
bash -n script.sh

# Trace execution
bash -x script.sh

# Debug sections in the script
set -x  # Start debugging
# ... code to debug ...
set +x  # Stop debugging