Bash Ripple Effect: Pipe Stack

This lesson turns individual commands into a stack. You first filter a stream, then count the filtered result in the same command chain.

cat events.log | grep warn
cat events.log | grep warn | wc -l

The first command returns matching lines. The second returns only the numeric count:

warn: queue
warn: retry
2

Pipes let each command do one job well. This composability is core to Bash productivity and keeps complex workflows understandable.

• Running wc -l on full input instead of filtered input.
• Forgetting spaces around |, causing parse errors.
• Skipping validation of intermediate output.

Save the count for reporting:

cat events.log | grep warn | wc -l > warn-count.txt
cat warn-count.txt

This bridges analysis and documentation in one lightweight flow.