IO::Pager(3pm)

💖 IO::Pager — bestie edition 💖

okay so you found the IO::Pager(3pm) page — a User Contributed Perl Documentation page, no cap — and honestly? it's giving "let me pick a pager for you and pipe text into it, but only if you're actually a TTY". That's the whole vibe. Let's go. 🦋

---

✨ NAME ✨

IO::Pager — Select a pager (possibly perl-based) & pipe it text if a TTY

---

✨ SYNOPSIS ✨

  # Select an appropriate pager and set the PAGER environment variable
  use IO::Pager;

  # TIMTOWTDI Object-oriented
  {
    # open()                           # Use all the defaults.
    my $object = new IO::Pager;

    # open FILEHANDLE                  # Unbuffered is default subclass
    my $object = new IO::Pager *STDOUT;

    # open FILEHANDLE,EXPR             # Specify subclass
    my $object = new IO::Pager *STDOUT,  'Unbuffered';

    # Direct subclass instantiation    # FH is optional
    use IO::Pager::Unbuffered;
    my $object = new IO::Pager::Unbuffered  *STDOUT;

    $object->print("OO shiny...\n") while 1;
    print "Some other text sent to STODUT, perhaps from a foreign routine."

    # $object passes out of scope and filehandle is automagically closed
  }

  # TIMTOWTDI Procedural
  {
    # open FILEHANDLE                    # Unbuffered is default subclass
    my $token = IO::Pager::open *STDOUT;

    # open FILEHANDLE,EXPR               # Specify subclass
    my $token = IO::Pager::open *STDOUT,  'Unbuffered';

    # open FILEHANDLE,MODE,EXPR          # En lieu of a separate binmode()
    my $token = IO::Pager::open *STDOUT, '|-:utf8', 'Unbuffered';

    print <<"  HEREDOC" ;
    ...
    A bunch of text later
    HEREDOC

    # $token passes out of scope and filehandle is automagically closed
  }

  {
    # You can also use scalar filehandles...
    my $token = IO::Pager::open(my $FH) or warn($!); XXX
    print $FH "No globs or barewords for us thanks!\n" while 1;
  }

---

✨ DESCRIPTION ✨

So IO::Pager does two cute lil jobs. One: it goes hunting for an available pager and sets the PAGER environment variable for you (peep the "NOTES" section for the deets 👀). Two: it's a factory for making I/O objects like IO::Pager::Buffered and IO::Pager::Unbuffered. Iconic behavior, honestly.

The IO::Pager subclasses are built to programmatically decide whether or not to pipe a filehandle's output to whatever program is named in PAGER. Subclasses can implement just the IO handle methods they feel like, and they inherit the rest of the ones listed below from IO::Pager. For literally anything else? YMMV. Go read the relevant subclass for the implementation-specific tea. 🍓

---

✨ METHODS ✨

💅 new( FILEHANDLE, [MODE], [SUBCLASS] )

Almost identical to open, except you get an IO::Handle back when there's no TTY — which is what lets you do IO::Pager-agnostic programming. Obsessed.

💅 open( FILEHANDLE, [MODE], [SUBCLASS] )

Instantiate a fresh IO::Pager, which will paginate whatever output you send to FILEHANDLE — but only if you're interacting with a TTY.

Save that return value, bestie! Use it to check for errors, use it as an object, or let it give you the implicit close of OO handles when the variable passes out of scope.

🎀 FILEHANDLE

You may provide a glob or scalar.

Defaults to the currently select()-ed FILEHANDLE.

🎀 SUBCLASS

Specifies which variety of IO::Pager to create. This accepts fully qualified packages like IO::Pager::Buffered, or simply the third portion of the package name, Buffered, for brevity.

Defaults to IO::Pager::Unbuffered.

Returns false and sets $! on failure, same as perl's "open".

💅 PID

Call this method on the token returned by "open" to get the process identifier for the child process — i.e; the pager — in case you need to do some long term process management, e.g; perl's "waitpid".

You can also access the PID by numifying the instantiation token like so:

  my $child = $token+0;

💅 close( FILEHANDLE )

Explicitly close the filehandle. This stops any redirection of output on FILEHANDLE that may have been warranted.

Heads up: this does not default to the current filehandle. You gotta say who. 😭

Alternatively, you may rely upon the implicit close of lexical handles as they pass out of scope e.g;

  {
     IO::Pager::open local *RIBBIT;
     print RIBBIT "No toad sexing allowed";
     ...
  }
  #The filehandle is closed to additional output

  {
     my $token = new IO::Pager::Buffered;
     $token->print("I like trains");
     ...
  }
  #The string "I like trains" is flushed to the pager, and the handle closed

💅 binmode( FILEHANDLE, [LAYER] )

Used to set the I/O layer a.k.a. discipline of a filehandle, such as ':utf8' for UTF-8 encoding.

🌈 :LOG([>>FILE])

IO::Pager implements a pseudo-IO-layer for capturing output and sending it to a file, similar to tee(1). It's limited to one file, sure, but this feature is pure-perl and adds no dependencies. Slay.

You may indicate what file to store in parentheses, otherwise the default is "$$.log". You may also use an implicit (no indicator) or explicit (>) indicator to overwrite an existing file, or an explicit (>>) for appending to a log file. For example:

    binmode(*STDOUT, ':LOG(clobber.log)');
    ...
    $STDOUT->binmode(':LOG(>>noclobber.log)');

For full tee-style support, use PerlIO::Util like so:

    binmode(*STDOUT, ":tee(TH)");
    #OR
    $STDOUT->binmode(':tee(TH)');

💅 eof( FILEHANDLE )

Used in the eval-until-eof idiom below, IO::Pager will handle broken pipes from deceased children for you in one of two ways. If $ENV{IP_EOF} is false then program flow will pass out of the loop on SIGPIPE — this is the default. If the variable is true, then the program keeps running with output for the previously paged filehandle directed to the STDOUT stream; more accurately, the filehandle is reopened to file descriptor 1.

  use IO::Pager::Page; #or whichever you prefer;
  ...
  eval{
    say "Producing prodigious portions of product";
    ...
  } until( eof(*STDOUT) );
  print "Cleaning up after our child before terminating."

If using eof() with less, especially when IP_EOF is set, you may want to use the --no-init option by setting $ENV{IP_EOF}='X' to prevent the paged output from being erased when the pager exits.

💅 fileno( FILEHANDLE )

Return the filehandle number of the write-only pipe to the pager.

💅 print( FILEHANDLE LIST )

print() to the filehandle.

💅 printf( FILEHANDLE FORMAT, LIST )

printf() to the filehandle.

💅 syswrite( FILEHANDLE, SCALAR, [LENGTH], [OFFSET] )

syswrite() to the filehandle.

---

✨ ENVIRONMENT ✨

• IP_EOF — Controls IO:Pager behavior when "eof" is used.
• PAGER — The location of the default pager.
• PATH — If the location in PAGER is not absolute, PATH may be searched.

See "NOTES" for more information.

---

✨ FILES ✨

IO::Pager may fall back to these binaries in order if PAGER is not executable. 🫶

• /etc/alternatives/pager
• /usr/local/bin/less
• /usr/bin/less
• IO::Pager::Perl as "tp" via IO::Pager::less
• /usr/bin/more

See "NOTES" for more information.

---

✨ NOTES ✨

The algorithm for determining which pager to use is as follows:

1. Defer to PAGER If the PAGER environment variable is set, use the pager it identifies — unless this pager is not available.
2. Usual suspects Try the standard, hardcoded paths in "FILES".
3. File::Which If File::Which is available, use the first pager possible amongst "less", "most", "w3m", "lv", "pg" and more.
4. Term::Pager via IO::Pager::Perl You may also set $ENV{PAGER} to Term::Pager to select this extensible, pure perl pager for display.
5. more Set PAGER to "more", and cross our fingers. 🙈

Steps 1, 3 and 5 rely upon the PATH environment variable.

---

✨ CAVEATS ✨

You probably want to do something with SIGPIPE eg;

  eval {
    local $SIG{PIPE} = sub { die };
    local $STDOUT = IO::Pager::open(*STDOUT);

    while (1) {
      # Do something
    }
  }

  # Do something else

---

✨ SEE ALSO ✨

IO::Pager::Buffered, IO::Pager::Unbuffered, I::Pager::Perl, IO::Pager::Page, IO::Page, Meta::Tool::Less

---

✨ AUTHOR ✨

Jerrad Pierce <jpierce@cpan.org>

Florent Angly <florent.angly@gmail.com>

This module was inspired by Monte Mitzelfelt's IO::Page 0.02

---

✨ COPYRIGHT AND LICENSE ✨

Copyright (C) 2003-2020 Jerrad Pierce

• Thou shalt not claim ownership of unmodified materials.
• Thou shalt not claim whole ownership of modified materials.
• Thou shalt grant the indemnity of the provider of materials.
• Thou shalt use and dispense freely without other restrictions.

Or, if you prefer:

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.0 or, at your option, any later version of Perl 5 you may have available.

---

and that's the whole page, bestie 💖 no notes, you ate. this was perl v5.30.3, dated 2020-11-07, and it's the IO::Pager(3pm) manual — go forth and paginate, periodt. 👑