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Recipe 8.25 Program: tctee

Not all systems support the classic tee program for splitting output pipes to multiple destinations. This command sends the output from someprog to /tmp/output and to the mail pipe beyond:

% someprog | tee /tmp/output | Mail -s "check this"

This program helps not only users who aren't on Unix systems and don't have a regular tee; it also helps those who are, because it offers features not found on other versions of tee.

The four flag arguments are -i to ignore interrupts, -a to append to output files, -u for unbuffered output, and -n to omit copying the output on to standard out.

Because this program uses Perl's magic open, you can specify pipes as well as files.

% someprog | tctee f1 "|cat -n" f2 ">>f3"

That sends the output from someprog to the files f1 and f2, appends it to f3, sends a copy to the program cat -n, and also produces the stream on standard output.

The program in Example 8-8 is one of many venerable Perl programs written nearly a decade ago that still runs perfectly well. If written from scratch now, we'd probably use strict, warnings, and ten to thirty thousand lines of modules. But if it ain't broke . . .

Example 8-8. tctee
  # tctee - clone that groks process tees 
  # perl3 compatible, or better.
  while ($ARGV[0] =~ /^-(.+)/ && (shift, ($_ = $1), 1)) {
      next if /^$/;
      s/i// && (++$ignore_ints, redo);
      s/a// && (++$append,      redo);
      s/u// && (++$unbuffer,    redo);
      s/n// && (++$nostdout,    redo);
      die "usage $0 [-aiun] [filenames] ...\n";
  if ($ignore_ints) {
      for $sig ("INT", "TERM", "HUP", "QUIT") { $SIG{$sig} = "IGNORE"; }
  $mode = $append ? ">>" : ">";
  $fh = "FH000";
  unless ($nostdout) {
      %fh = ("STDOUT", "standard output"); # always go to stdout
  $| = 1 if $unbuffer;
  for (@ARGV) {
      if (!open($fh, (/^[^>|]/ && $mode) . $_)) {
          warn "$0: cannot open $_: $!\n"; # like sun's; i prefer die
      select((select($fh), $| = 1)[0]) if $unbuffer;
      $fh{$fh++} = $_;
  while (<STDIN>) {
      for $fh (keys %fh) {
          print $fh $_;
  for $fh (keys %fh) {
      next if close($fh) || !defined $fh{$fh};
      warn "$0: couldnt close $fh{$fh}: $!\n";
  exit $status;
  sub PLUMBER {
      warn "$0: pipe to \"$fh{$fh}\" broke!\n";
      delete $fh{$fh};
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