🌍 Portability

Portable scripts work consistently across different Unix-like systems and shells. This section outlines best practices to achieve compatibility.

🧭 Why Care About Portability?

Different systems ship with varying combinations of: - Shells (sh, bash, zsh, dash) - Utilities (grep, sed, find) - Library versions and capabilities

Portable code avoids assumptions and uses widely supported constructs.

🧪 Best Practices

Stick to POSIX Compliance

POSIX defines minimal required features. Scripts using only POSIX constructs are highly portable.

Check compliance with tools like checkbashisms or shellcheck.

Example:

# ✅ POSIX compliant
[ -f "$file" ] && echo "exists"

# ❌ Bashism
[[ -f "$file" ]] && echo "exists"

Prefer External Tools Over Built-ins

Many built-in features vary between shells:

# ✅ More portable
expr 2 + 3

# ❌ Less portable
echo $((2+3))

Though arithmetic expansion is widely supported today.

🧰 Portable Alternatives Table

Feature	Portable Way	Non-portable Example
String comparison	`[ "$a" = "$b" ]`	`[[ "$a" == "$b" ]]`
Regex matching	`case` statement	`[[ "$a" =~ regex ]]`
Arrays	Use separate files or delimited strings	Native arrays in bash/zsh
Arithmetic	`expr`, external calculator	`$(( ))`
Process substitution	Avoid or simulate with temp files	`<()`

🧾 Summary

Aim for POSIX compliance whenever possible.
Avoid shell-specific extensions unless absolutely necessary.
Test scripts in multiple environments.
Document known dependencies clearly.

👉 Proceed to: Extended Parameters and Expansions