Use when writing shell scripts that need to run across different systems, shells, or environments. Covers POSIX compatibility and platform differences.
Limited to specific tools
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This skill is limited to using the following tools:
name: shell-portability description: Use when writing shell scripts that need to run across different systems, shells, or environments. Covers POSIX compatibility and platform differences. allowed-tools:
Techniques for writing shell scripts that work across different platforms and environments.
#!/usr/bin/env bash
# Most portable for bash scripts
# Works on Linux, macOS, BSD
#!/bin/sh
# For maximum portability
# Use only POSIX features
# Bash - arrays available
declare -a items=("one" "two" "three")
for item in "${items[@]}"; do
echo "$item"
done
# POSIX - use positional parameters or space-separated strings
set -- one two three
for item in "$@"; do
echo "$item"
done
# Bash - extended test
if [[ "$var" == "value" ]]; then
echo "match"
fi
# POSIX - basic test
if [ "$var" = "value" ]; then
echo "match"
fi
# Bash - regex matching
if [[ "$input" =~ ^[0-9]+$ ]]; then
echo "numeric"
fi
# POSIX - use case or external tools
case "$input" in
*[!0-9]*|'') echo "not numeric" ;;
*) echo "numeric" ;;
esac
# Bash - arithmetic expansion
(( count++ ))
if (( count > 10 )); then
echo "greater"
fi
# POSIX - expr or arithmetic expansion
count=$((count + 1))
if [ "$count" -gt 10 ]; then
echo "greater"
fi
# Date command differences
# GNU (Linux)
date -d "yesterday" +%Y-%m-%d
# BSD (macOS)
date -v-1d +%Y-%m-%d
# Portable approach
if date --version >/dev/null 2>&1; then
# GNU date
yesterday=$(date -d "yesterday" +%Y-%m-%d)
else
# BSD date
yesterday=$(date -v-1d +%Y-%m-%d)
fi
# GNU sed - in-place edit
sed -i 's/old/new/g' file.txt
# BSD sed - requires backup extension
sed -i '' 's/old/new/g' file.txt
# Portable approach
sed 's/old/new/g' file.txt > file.txt.tmp && mv file.txt.tmp file.txt
# Or use a function
sed_inplace() {
if sed --version >/dev/null 2>&1; then
sed -i "$@"
else
sed -i '' "$@"
fi
}
# GNU readlink
readlink -f /path/to/link
# BSD/macOS - no -f option by default
# Use greadlink from coreutils or:
resolve_path() {
local path="$1"
if command -v greadlink >/dev/null 2>&1; then
greadlink -f "$path"
elif command -v realpath >/dev/null 2>&1; then
realpath "$path"
else
# Fallback
cd "$(dirname "$path")" && pwd -P
fi
}
detect_os() {
case "$(uname -s)" in
Linux*) echo "linux" ;;
Darwin*) echo "macos" ;;
MINGW*|CYGWIN*|MSYS*) echo "windows" ;;
FreeBSD*) echo "freebsd" ;;
*) echo "unknown" ;;
esac
}
OS=$(detect_os)
case "$OS" in
linux) INSTALL_CMD="apt-get install" ;;
macos) INSTALL_CMD="brew install" ;;
esac
detect_arch() {
case "$(uname -m)" in
x86_64|amd64) echo "amd64" ;;
aarch64|arm64) echo "arm64" ;;
armv7l) echo "arm" ;;
*) echo "unknown" ;;
esac
}
detect_shell() {
if [ -n "$BASH_VERSION" ]; then
echo "bash"
elif [ -n "$ZSH_VERSION" ]; then
echo "zsh"
else
echo "sh"
fi
}
# Portable line reading
while IFS= read -r line || [ -n "$line" ]; do
echo "$line"
done < "$file"
# The || [ -n "$line" ] handles files without trailing newline
# POSIX-compatible temp file
make_temp() {
if command -v mktemp >/dev/null 2>&1; then
mktemp
else
# Fallback
local tmp="/tmp/tmp.$$.$RANDOM"
touch "$tmp" && echo "$tmp"
fi
}
# POSIX-compatible command check
has_command() {
command -v "$1" >/dev/null 2>&1
}
# Usage
if has_command curl; then
curl "$url"
elif has_command wget; then
wget -O- "$url"
else
echo "No HTTP client available" >&2
exit 1
fi
# POSIX-compatible string contains
contains() {
case "$1" in
*"$2"*) return 0 ;;
*) return 1 ;;
esac
}
# Usage
if contains "$PATH" "/usr/local/bin"; then
echo "Found in PATH"
fi
# When intentionally using non-portable features
# shellcheck disable=SC2039 # Bash-specific feature
if [[ "$var" =~ regex ]]; then
:
fi
# Document why
# shellcheck disable=SC2016 # Intentionally not expanding
echo 'Use $HOME for home directory'
#!/usr/bin/env bash
# shellcheck shell=bash
# Or for POSIX:
#!/bin/sh
# shellcheck shell=sh
#!/usr/bin/env bash for bash scripts