Shell Scripting Deep Dive Cheat Sheet

Advanced Bash scripting patterns including parameter expansion, error handling, arrays, and safe scripting practices.

2 PagesAdvancedJan 28, 2026

Strict Mode & Error Handling

Make scripts fail fast and loudly.

bash

#!/usr/bin/env bashset -euo pipefailIFS=$'\n\t'# -e: exit on any command failure# -u: error on unset variables# -o pipefail: fail if any command in a pipeline failstrap 'echo "Error on line $LINENO" >&2' ERR

Parameter Expansion

Common Bash string/variable manipulations.

bash

name=${1:-default}          # Default value if $1 unset/emptyfile=${path##*/}            # Strip longest match from front (basename)dir=${path%/*}              # Strip shortest match from back (dirname)upper=${str^^}               # Uppercase entire stringlen=${#str}                  # String lengthsub=${str:0:5}               # Substring (offset, length)replaced=${str//foo/bar}     # Replace all occurrences

Arrays & Loops

Working with indexed arrays and iteration.

bash

arr=(one two three)for item in "${arr[@]}"; do    echo "$item"doneecho "Count: ${#arr[@]}"# Read a file line by line safelywhile IFS= read -r line; do    echo "$line"done < input.txt

Common Gotchas

Mistakes that cause subtle bugs.

Unquoted variables- Always quote "$var" to prevent word splitting and glob expansion
[ vs [[- Prefer [[ ]] in Bash for safer comparisons and pattern matching support
$(cmd) vs `cmd`- Prefer $() for command substitution; it nests cleanly and is more readable
local in functions- Declare function variables with 'local' to avoid leaking into global scope
set -e pitfalls- set -e does not trigger inside conditionals like 'if cmd; then' — errors there must be checked explicitly
shellcheck- Static analysis tool that catches quoting, portability, and logic bugs before runtime

Pro Tip

Run every script through 'shellcheck' in CI — it catches the exact class of quoting and word-splitting bugs that cause scripts to work in testing but fail unpredictably in production.

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