head: Usage, Options & Common CI Errors

head shows the beginning of a file or stream - the first 10 lines by default.

head is a trivial command with one non-trivial CI interaction: when it closes a pipe early, the upstream process gets SIGPIPE, which with set -o pipefail can fail the step.

What it does

head outputs the first part of each input - by default the first 10 lines, or a chosen number of lines (-n) or bytes (-c). It is commonly used to preview files or cap output.

Common usage

Terminal

head file.txt                  # first 10 lines
head -n 5 file.txt
head -n -3 file.txt            # all but the last 3 (GNU)
head -c 100 file.bin          # first 100 bytes
some_command | head -n 20

Options

Flag	What it does
-n <N>	First N lines (-N also works)
-n -<N>	All but the last N lines (GNU)
-c <N>	First N bytes
-q / -v	Never / always print file headers

Common errors in CI

When head exits after N lines it closes the pipe, sending SIGPIPE to the producer; that producer exits 141 (128+13). With set -o pipefail, cmd | head can therefore make the whole pipeline "fail" even though it worked - handle it deliberately (e.g. cmd | head || true, or restructure). Negative counts (head -n -3) and -c byte mode are GNU features absent on some BSD/BusyBox builds.

Related guides

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