Linux Basic — Optimizing Scripts Practice

Practice Exercises — Optimizing Scripts

Measure, optimise, and measure again.

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Warm-up

1. Replace cat file | grep pattern with grep pattern file.
2. Replace echo "$var" | cmd with cmd <<< "$var".
3. Replace if [ "$x" = "y" ] with if [[ "$x" == "y" ]].
4. Replace result=$(expr $a + $b) with result=$((a + b)).

Builtins vs External

1. Use ${file##*/} instead of basename "$file".
2. Use ${file%/*} instead of dirname "$file".
3. Replace for i in $(seq 1 1000) with for i in {1..1000}.
4. Use command -v instead of which.

Arrays

1. Use mapfile -t lines < file to read a file into an array.
2. Refactor a loop that splits a string on every iteration to split once into an array.

Profiling

1. Use time to measure a script’s real/user/sys time.
2. Use /usr/bin/time -v to see memory usage (Linux).
3. Enable per-line tracing with PS4 and find the slowest line.
4. Use SECONDS=0 to time a function.

Parallelism

1. Convert a serial loop that processes 100 files into xargs -P 4.
2. Use find -print0 | xargs -0 for files with spaces.
3. Parallelise the same task with GNU parallel -j 8 --bar.
4. Export a Bash function and call it from parallel.

Real Scenario

1. Take a script that runs grep inside a loop over 1,000 files. Refactor to one grep -r or xargs grep.
2. Take a 10-second script, profile it, identify the bottleneck, apply one optimisation from this chapter, and verify the speedup.

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Verification Checklist

• Benchmarked before and after (time output)
• No unnecessary forks in hot loops
• Builtins used where possible
• Parallelism applied to I/O-bound or CPU-bound independent tasks
• -print0 / -0 used for safe filename handling

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You’ve Completed Linux Basics!

You now have the tools to write correct, maintainable, and fast Bash scripts. From here:

• Build automation for your own workflows
• Contribute to open-source shell projects
• Explore advanced topics: network scripting, parsing complex formats, or bridging Bash with Python/Go

Keep scripting, and remember: clarity first, then correctness, then speed.