Loops and Lists

Arrays

Multiple Values

Bash arrays store several words under one variable name. Indexes start at zero.

Program

Play the script to watch an array provide one element and a count.

arrays.sh
Replay: real traced execution (multi-file project)
#!/usr/bin/env bash

tasks=("lint" "test" "package")
first="${tasks[0]}"
count="${#tasks[@]}"
echo "$first/$count"

  1. tasks ← [lint, test, package]

    3tasks=("lint" "test" "package")4first="${tasks[0]}"
    values this step[lint, test, package]tasks

  2. first ← lint

    3tasks=("lint" "test" "package")4first="${tasks[0]}"5count="${#tasks[@]}"
    values this steplintfirstlinttasks[0]

  3. count ← 3

    4first="${tasks[0]}"5count="${#tasks[@]}"6echo "$first/$count"
    values this step3count[lint, test, package]tasks

  4. echo "$first/$count"

    5count="${#tasks[@]}"6echo "$first/$count"
    outputlint/3
    values this steplintfirst3count

Read One Element

  1. tasks stores lint, test, and package.
  2. Bash array indexes start at 0.
  3. ${tasks[0]} reads lint.
  4. ${#tasks[@]} counts all three tasks.
  5. The script prints lint/3. | Index | Task | | --- | --- | | 0 | lint | | 1 | test | | 2 | package |
array An array stores multiple values and retrieves each by index.
array length `${#array[@]}` expands to the number of array elements.

Exercise: arrays.sh

Read the first task from an array, count all tasks, and print both values