•Updated•Arnošt Havelka
Bash Ripple Effect: Pipe Stack
Chain cat, grep, and wc into a repeatable multi-stage text processing stack.
Start Interactive Lesson
This lesson turns individual commands into a stack. You first filter a stream, then count the filtered result in the same command chain.
Commands to Practice
printf '%s\n' 'warn: slow' 'info: retry' 'warn: timeout' > events.log
cat events.log | grep warn
cat events.log | grep warn | wc -l
Expected Terminal Signal
The first command returns matching lines. The second returns only the numeric count:
warn: queue
warn: retry
2
Why This Matters
Pipes let each command do one job well. This composability is core to Bash productivity and keeps complex workflows understandable.
Common Mistakes
- Running
wc -lon full input instead of filtered input. - Forgetting spaces around
|, causing parse errors. - Skipping validation of intermediate output.
Practice Extension
Save the count for reporting:
printf '%s\n' 'warn: slow' 'info: retry' 'warn: timeout' > events.log
cat events.log | grep warn | wc -l > warn-count.txt
cat warn-count.txt
This bridges analysis and documentation in one lightweight flow.
References
These documentation links provide authoritative details for the commands used in this article.
Up Next
Bash Ripple Practice: Incident Combo
Run a two-step incident extraction and counting workflow with reproducible outputs.