Bash Scripting — Iterating Through Lists
Welcome to Chapter 22 — Iterating Through Lists 🔁
Loops are the backbone of automation. In this chapter, you’ll master every way Bash lets you walk through collections — arrays, files, command output, glob patterns, and the powerful find/xargs duo.
By the end, you’ll handle any list Bash throws at you — safely, efficiently, and without the classic pitfalls that trip up even experienced scripters.
What You’ll Learn
| Lesson | Topic | Key Takeaway |
|---|---|---|
| 01 — Looping Array Elements | Arrays | for, while, indexed, parallel |
| 02 — Looping Directory Listings | Files & Dirs | Globs, find -print0, safe iteration |
| 03 — Looping Command Output | Commands | while read, process substitution, mapfile |
| 04 — Glob Patterns in Scripts | Globs | extglob, nullglob, failglob |
| 05 — find and xargs Pattern | find/xargs | -exec, -print0, parallel xargs |
| 06 — Practice Exercises | Exercises | 5 hands-on challenges |
Why This Chapter Matters
Almost every real-world script needs to process a collection:
- Deploy configs to N servers
- Resize every image in a folder
- Parse every line of a log file
- Act on every pod returned by
kubectl
Getting iteration wrong leads to broken scripts when filenames contain spaces, when lists are empty, or when output changes format. This chapter teaches you the safe patterns.
The Golden Rules of Bash Iteration
#!/usr/bin/env bash
set -euo pipefail
# Rule 1: Quote your expansions
for item in "${array[@]}"; do echo "$item"; done
# Rule 2: Use `while read` for line-by-line command output
some_command | while IFS= read -r line; do echo "$line"; done
# Rule 3: Use find -print0 | xargs -0 for filenames
find /path -name '*.log' -print0 | xargs -0 rm -f
# Rule 4: Enable nullglob when globbing might match nothing
shopt -s nullglob
Quick Decision Guide
Need to iterate over...
│
├── An array? → Lesson 01
├── Files in a dir? → Lesson 02
├── Command output? → Lesson 03
├── Pattern matches? → Lesson 04
├── Deep file trees? → Lesson 05
└── Need practice? → Lesson 06
Prerequisites
Make sure you’re comfortable with:
- Loops —
for,while,until(Chapter 20) - Arrays — indexed & associative (Chapter 21)
- Quoting — double vs single quotes
Let’s Begin
Start with Lesson 01 — Looping Array Elements →
Happy scripting! 🚀
