Halt a Shell Pipe Once Any Chain is Finished-CodePudding

Is it possible on such a pipe line

tee stdin.log | subject-command | tee stdout.log

to halt an execution once subject-command is finished.

Instead as I experience it the first tee proceeds while its income stream goes on.

CodePudding user response：

Behavior of tee varies by operating system. When given multiple explicit file outputs it keeps going until all of them have failed; whether it should exit immediately when stdout failed is somewhat open to interpretation in the standard defining its behavior. (I'd argue that failing to exit in this case is a bug and should be reported to your OS vendor, but that doesn't help you when you have a problem now).

Assuming bash 4.1 or newer, and that you're processing line-oriented textual content that doesn't contain any NULs:

mytee() {
  local arg new_fd
  local -a fds=( )

  # open our output files
  for arg in "$@"; do
    exec {new_fd}>"$arg"
    fds =( "$new_fd" )
  done

  # loop over input until first failure
  while IFS= read -r line; do
    for fd in "${fds[@]}"; do
      printf '%s\n' "$line" >&"$fd" || break
    done
    printf '%s\n' "$line" || break
  done

  # close our output files
  for fd in "${fds[@]}"; do
    exec {fd}>&-
  done
}

...the problem described in this question will no longer occur with:

mytee stdin.log | subject-command | tee stdout.log

CodePudding user response：

Ignoring the issues specific to tee, we can work around this with process substitutions (another ksh/zsh/bash feature not available in sh).

This too requires a relatively recent bash release and isn't compatible with sh (as process substitutions didn't set $! until release 4.3 or so).

#!/usr/bin/env bash
#              ^^^^- only bash, not sh

exec {stdin_log_tee_fd}< <(tee stdin.log); stdin_log_tee_pid=$!
subject-command <&$stdin_log_tee_fd | tee stdout.log
kill "$stdin_log_tee_pid"