Linux Basic — Manipulating Arrays

Manipulating Arrays

Bash has two array types: indexed (numeric keys) and associative (string keys). They’re more powerful than most scripters realise — and they’re the cleanest way to handle lists of filenames, sets of unique values, key/value lookup tables, and ordered command arguments.

This chapter is the full tour.

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What You Will Learn

By the end of this chapter you will be able to:

• Create, read, update, and delete entries in indexed arrays
• Use associative arrays (Bash 4+) as in-memory hash maps
• Slice arrays and make safe copies
• Sort arrays alphabetically or numerically (Bash + sort)
• Know exactly when to use an array vs a string and avoid the classic for x in $list bug

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Topics in This Chapter

#	Topic	Description
1	Indexed Array CRUD	declare, append, read, delete
2	Associative Array CRUD	declare -A, key/value, iterate
3	Array Slicing & Copying	${arr[@]:1:3}, deep copy
4	Sorting Arrays	native + sort integration
5	Array vs String	why "$@" ≠ $*; quoting rules
6	Practice Exercises	Hands-on tasks

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Quick Mental Model

# Indexed — integer keys, ordered
fruits=(apple banana cherry)
echo "${fruits[0]}"        # apple

# Associative — string keys, unordered (Bash 4+)
declare -A user
user[name]=alice
user[role]=admin
echo "${user[name]}"       # alice

Two rules to memorise:

1. ${arr[@]} with the "@" and quotes is the safe way to expand all elements — each as its own word.
2. ${arr[*]} joins all elements with the first char of IFS. Useful for printing, dangerous for iterating.

We’ll go deep on this in the Array vs String page.

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Next → Indexed Array CRUD