Broken pipe

What happens

SIGPIPE is delivered when a command writes to a pipe whose reading end has already exited. Default behaviour is to terminate.

ps aux | head -1

head exits after one line and ps gets SIGPIPE writing the rest. That is normal, not a fault.

set +o pipefail
command | head -1 || true

128 plus 13. A script checking for non-zero will treat this as failure even though the pipeline worked.

Scope: failure mode: SIGPIPE when a pipeline consumer exits early.

CliHelper documents failure modes of third-party command line tools. No software is stored or distributed here.