Shell script best practices
Follow these shell script best practices when writing or modifying bash scripts:
1. Use #!/usr/bin/env bash instead of #!/bin/bash for better portability
Bad:
`bash
!/bin/bash
echo "Hello World"
`
Good:
`bash
!/usr/bin/env bash
echo "Hello World"
`
2. Use ${variable} syntax for all variable references
Bad:
`bash
name="Alice"
echo "Hello $name"
`
Good:
`bash
name="Alice"
echo "Hello ${name}"
`
3. Use double quotes around variable expansions to prevent word splitting and globbing
Bad:
`bash
files=$(ls)
for file in $files; do
rm $file
done
`
Good:
`bash
files=$(ls)
for file in "${files}"; do
rm "${file}"
done
`
4. Use [[ and ]] instead of [ and ] for conditional expressions
Bad:
`bash
if [ -z "$input" ] || [ "$input" = "exit" ]; then
echo "Exiting..."
exit 0
fi
`
Good:
`bash
if [[ -z "${input}" || "${input}" = "exit" ]]; then
echo "Exiting..."
exit 0
fi
`
5. Use printf '%s\n' instead of echo for output with special characters
Bad:
`bash
output="Text with special chars: * & $HOME"
echo $output
`
Good:
`bash
output="Text with special chars: * & $HOME"
printf '%s\n' "${output}"
`
6. Use readonly for constants that should not be modified
Bad:
`bash
CONFIG_PATH="/etc/app/config.json"
LOG_DIR="/var/log/app"
`
Good:
`bash
readonly CONFIG_PATH="/etc/app/config.json"
readonly LOG_DIR="/var/log/app"
`
7. Use | as delimiter in sed commands when replacing paths containing slashes
Bad:
`bash
sed -i "s/${source_path}/${target_path}/" "${config_file}"
`
Good:
`bash
sed -i "s|${source_path}|${target_path}|" "${config_file}"
`
