cross-platform-compat

name	cross-platform-compat
description	Portable bash patterns for Windows Git Bash, Linux, and macOS. Canonical replacement table for bc/python3/nproc/sed-i/git-add and OS detection. Use when writing or auditing scripts that run across machines.
version	1.0.0
category	_core/bash
type	skill
trigger	manual
auto_execute	false
platforms	["linux","macos","windows_gitbash"]
capabilities	["cross_platform","windows_gitbash_compat","portable_arithmetic","python_resolver","os_detection"]
tags	["bash","cross-platform","windows","git-bash","portable","bc","python3","nproc"]
related_skills	["bash-script-framework","bash-cli-framework"]

Cross-Platform Bash Compatibility

Canonical replacement patterns for shell constructs that break on Windows Git Bash, macOS, or both. Always use these patterns in workspace-hub scripts.

Quick Reference — Replacement Table

Broken Pattern	Breaks On	Portable Replacement
echo "$a < $b" | bc -l	Git Bash (no bc)	awk "BEGIN {print ($a < $b) ? 1 : 0}"
echo "scale=2; $a / $b" | bc	Git Bash	awk "BEGIN {printf \"%.2f\", $a / $b}"
python3 script.py	Windows	$PYTHON script.py (use resolver below)
nproc	Git Bash	nproc 2>/dev/null || getconf _NPROCESSORS_ONLN 2>/dev/null || echo 1
sed -i "s/..."	macOS	sed -i.bak "s/..." && rm file.bak
git add missing/dir/	all (set -e)	Guard with [[ -d path ]] && git add path
date -v-1d +%Y%m%d	Linux/Git Bash	date -d "yesterday" +%Y%m%d 2>/dev/null || date -v-1d +%Y%m%d

Patterns in Detail

Float Comparison Without bc

# bc not available on Git Bash Windows
# BAD:  if (( $(echo "$score < 0.6" | bc -l) )); then
# GOOD: awk-based (works everywhere)
float_lt() {
    awk "BEGIN {exit !($1 < $2)}"
}
if float_lt "$score" "0.6"; then echo "below threshold"; fi

# Or integer-multiply trick (score 0.0-1.0 → multiply by 10):
score_int=$(awk )
 (( score_int <  ));   ;