bash-portability

Bash Portability

Guidance for writing portable POSIX-compatible scripts and understanding when to leverage bash-specific features.

Shebang Selection

Use #!/usr/bin/env bash for Bash Scripts

#!/usr/bin/env bash

Why: Searches PATH for bash, works across systems where bash may be in different locations.

Use #!/bin/sh for POSIX Scripts

#!/bin/sh

Why: Maximum portability when bash features aren't needed. On many systems, /bin/sh is dash or another POSIX shell.

Direct Path When Required

#!/bin/bash

Use only when: System requirements guarantee bash location, or security policy requires absolute paths.

POSIX vs Bash Feature Matrix

| Feature | POSIX | Bash | Recommendation | | -------------- | ------- | ---- | ------------------------------ | ---- | | [[ ]] | No | Yes | Use [ ] for POSIX | | (( )) | No | Yes | Use [ ] with -eq etc. | | Arrays | No | Yes | Use positional params or files | | local | Partial | Yes | Generally safe | | ${var,,} | No | 4+ | Use tr for POSIX | | <<< | No | Yes | Use echo | cmd | | =~ regex | No | Yes | Use grep or expr | | source | No | Yes | Use . (dot) command | | function f() | No | Yes | Use f() only | | $'...' | No | Yes | Use printf | | {1..10} | No | Yes | Use seq or while loop |

POSIX-Compatible Patterns

Conditionals

# POSIX - use [ ] with proper quoting
if [ -f "$file" ]; then
    echo "File exists"
fi

# String comparison
if [ "$var" = "value" ]; then
    echo "Match"
fi

# Numeric comparison
if [ "$num" -gt 10 ]; then
    echo "Greater"
fi

# Compound conditions
if [ -f "$file" ] && [ -r "$file" ]; then
    echo "Readable file"
fi