Source and Include: Reuse Code

Source lets you reuse code from other files. Like libraries. Write once. Use many times.

Here's the thing: Source makes scripts modular. Share functions. Avoid duplication. Use it.

Basic source

source functions.sh
. functions.sh                   # Same thing (shorthand)

The .: Shorthand for source. Same thing.

My take: Use . or source. Both work. . is shorter.

Example Library

functions.sh:

#!/bin/bash
# Common functions

log_info() {
    echo "[INFO] $*"
}

log_error() {
    echo "[ERROR] $*" >&2
}

backup_file() {
    local file="$1"
    cp "$file" "${file}.backup"
}

script.sh:

#!/bin/bash
source functions.sh

log_info "Script started"
backup_file "important.txt"
log_info "Script completed"

My take: Put common functions in a file. Source it. Reuse them.

Why Use source?

Benefits:

• Share functions across scripts
• Avoid code duplication
• Organize code
• Easier maintenance

My take: Source makes scripts cleaner. More maintainable. Use it.

Common Patterns

Shared Utilities

# utils.sh
log() {
    echo "[$(date)] $*"
}

error_exit() {
    echo "Error: $1" >&2
    exit 1
}

# script.sh
source utils.sh
log "Starting"

Configuration

# config.sh
SERVER="localhost"
PORT=8080
DEBUG=false

# script.sh
source config.sh
echo "Connecting to $SERVER:$PORT"

Common Mistakes (I've Made These)

1. Not using absolute paths: Relative paths break if you change directories. Use absolute paths or $SCRIPT_DIR.

2. Sourcing multiple times: Source runs the file. If it has side effects, they happen multiple times.

3. Circular dependencies: File A sources B, B sources A. Breaks things. Avoid it.

4. Not checking if file exists: Source fails if file doesn't exist. Check first.

5. Global variables: Sourced files share variables. Be careful with names.

Real-World Examples

Shared Logging

# lib/logger.sh
log() {
    local level="$1"
    shift
    echo "[$(date '+%Y-%m-%d %H:%M:%S')] [$level] $*"
}

# scripts/deploy.sh
source lib/logger.sh
log "INFO" "Deploying application"

Common Functions

# lib/common.sh
validate_file() {
    if [ ! -f "$1" ]; then
        echo "Error: File not found: $1"
        return 1
    fi
}

# scripts/backup.sh
source lib/common.sh
validate_file "$backup_file"

What's Next?

Now that you can reuse code, scripts become modular. Or learn about Automation Patterns to automate tasks.

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Personal note: When I started, I'd copy functions between scripts. Then I learned source. Now I put common functions in libraries. Scripts are cleaner. Easier to maintain. Source is worth it.