When Not to Use Bash, and Portability

Know the edges of the tool

Bash is excellent for gluing commands together: orchestration, file shuffling, deployment steps, CI tasks and quick automation. It becomes the wrong tool when a script needs complex data structures (nested maps, objects), floating-point maths, structured data beyond what jq handles comfortably, robust error handling across many steps, unit tests for intricate logic, concurrency beyond simple background jobs, or grows beyond a few hundred lines. At that point, Python, Go or another language usually gives clearer, safer code. A common rule of thumb from Google's shell style guide: if a script is more than about 100 lines or uses non-trivial control flow, consider rewriting it in a more structured language. For portability, decide your target: if a script must run under /bin/sh on minimal systems (Alpine's BusyBox, Debian's dash), write POSIX sh without arrays, [[ ]], local (not POSIX, though widely supported) or $(( ))-only features, and check with shellcheck --shell=sh. If you need Bash, require it explicitly and know which version: macOS's built-in 3.2 lacks associative arrays, mapfile and ${var,,}.

Bash-only features and POSIX alternatives

Useful when a script must run under /bin/sh.

bash feature                 POSIX sh alternative
---------------------------  ----------------------------------------------
[[ $a == b* ]]               case $a in b*) ... ;; esac
[[ -n $x && -f $f ]]         [ -n "$x" ] && [ -f "$f" ]
arrays: list=(a b c)         "$@" via set -- a b c, or newline-separated text
$(( i++ ))                   i=$((i + 1))
function f { local v; }      f() { v=...; }   (local is common but not POSIX)
<(cmd) process substitution  temporary files or named pipes (mkfifo)
${var^^}                     printf '%s' "$var" | tr '[:lower:]' '[:upper:]'
read -a, mapfile             while read loops

Duct tape and a toolbox

Bash is the best duct tape in the world: perfect for quickly joining things that were never designed to fit. But you would not build a house out of duct tape; at some point you reach for a proper toolbox.

Quick check: Which situation most strongly suggests rewriting a Bash script in Python or Go?

• The script runs three commands in order
• The script has grown to hundreds of lines with nested data structures and floating-point maths
• The script needs to set an environment variable
• The script uses a here-document