Interview › Scripting (Bash, Groovy)
What is a pipe, and how does data flow through a | b | c? [Intermediate]
Answer
A pipe connects the stdout of one command to the stdin of the next command. In a pipeline like a | b | c, data streams left to right through each process.
Technical explanation
Pipelines are ideal for Unix text processing because each command does one job and passes data onward.
By default, the pipeline exit status is usually the last command's exit status; set -o pipefail changes that behavior in Bash.
Each stage runs as a separate process, and shell state changes inside pipeline components may not persist in the parent shell.
Hands-on example
grep 'ERROR' app.log | awk '{print $1}' | sort | uniq -c | sort -rn
set -o pipefail
curl -fsS https://example.com/data | jq '.items[]'
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