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Documentation Index

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Arrays in Bash empower you to store multiple values in an indexed collection, offering direct access to any element—first, middle, or last—by its index. This is analogous to reaching into a specific drawer when you know exactly where your socks are kept, rather than inspecting each one sequentially.
The image illustrates the concept of arrays using a drawer analogy, showing three drawers labeled 1, 2, and 3 on the left, and an array with indices 0, 1, and 2 on the right.
Bash arrays are zero-indexed: the first element is at index 0, the second at 1, and so on.

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Why Use Arrays?

  • Direct element access reduces loops and conditional checks.
  • Cleaner scripts when handling lists of servers, filenames, or configurations.
  • Improved performance versus string-based lists requiring manual parsing.
Compare a string-based iteration: 
#!/usr/bin/env bash

servers="server1 server2 server3"
for server in ${servers}; do
  if [[ "$server" == "server2" ]]; then
    server="${server}.kodekloud.com"
  fi
  echo "$server"
done
Output: 
server1
server2.kodekloud.com
server3
This checks every item, akin to opening each drawer until you find your socks. Arrays eliminate that overhead.

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Declaring Arrays

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1. Assigning by Index

#!/usr/bin/env bash

course_sections[0]="Introduction"
course_sections[1]="Coding Standards"
course_sections[2]="Refresher"

echo "${course_sections[0]}"   # Introduction
echo "${course_sections[1]}"   # Coding Standards
echo "${course_sections[2]}"   # Refresher
The image illustrates an array with three indexed elements (0, 1, 2), highlighting the second element (index 1) as "server[1]".

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2. Inline Initialization

#!/usr/bin/env bash

declare -a course_sections=("Introduction" "Coding Standards" "Refresher")
echo "${course_sections[@]}"   # Introduction Coding Standards Refresher
You can also omit declare -a: 
course_sections=("Intro" "Middle" "End")

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Accessing Array Elements

OperationSyntaxExample Output
Single element${array[index]}${course_sections[1]} → Coding Standards
All elements${array[@]}${course_sections[@]} → all items
Number of elements${#array[@]}count of items
All indices (keys)${!array[@]}list of valid indices
Slice${array[@]:start:length}subset of elements

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Get All Elements

#!/usr/bin/env bash

sections=("Intro" "Body" "Conclusion")
echo "${sections[@]}"  # Intro Body Conclusion

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Quoting Arrays: Preserve Whitespace

Unquoted expansions split on spaces: 
#!/usr/bin/env bash

sections=("Coding Standards" "Best Practices")

# Unquoted
for s in ${sections[@]}; do
  echo "$s"
done

# Quoted
for s in "${sections[@]}"; do
  echo "$s"
done
Output: 
Coding
Standards

Coding Standards
Always quote ${array[@]} in loops or commands to preserve elements containing spaces.
Unquoted expansions can lead to unexpected word splitting.

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Modifying Arrays

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Append an Element

#!/usr/bin/env bash

sections=("Intro" "Methods")
sections+=("Conclusion")
echo "${sections[@]}"  # Intro Methods Conclusion

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Overwrite Entire Array

Assigning a string replaces index 0 but retains the array type: 
#!/usr/bin/env bash

sections=("A" "B" "C")
sections="NewSection"
echo "${sections[@]}"  # NewSection

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Further Reading and References

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