Plan 9's p pager

Useful for dumb terminals (e.g. `shell` under Emacs).

p

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+#!/usr/bin/env perl
+
+use strict;
+use warnings;
+
+my $pagesize = $ENV{'LINES'} || 22;
+
+open(my $tty, '<', '/dev/tty')
+    or die "$0: Cannot open /dev/tty for reading: $!";
+
+sub evalcmd {
+    {
+	chomp($_ = <$tty>);
+	if (/^q$/) {
+	    exit(0);
+	} elsif (/^!(.*)/) {
+	    system($1);
+	    redo;
+	}
+    }
+}
+
+sub printfile {
+    my ($fh) = @_;
+    my $lines = 0;
+    while (<$fh>) {
+	print;
+	&evalcmd unless ++$lines % $pagesize;
+    }
+    &evalcmd;
+}
+
+unshift(@ARGV, '-') unless @ARGV;
+
+for (@ARGV) {
+    if (/^-$/) {
+	&printfile(\*STDIN);
+    } elsif (/^-(\d+)$/) {
+	$pagesize = $1;
+    } else {
+	open(my $fh, '<', $_) or die "$0: Cannot open $_ for reading: $!";
+	&printfile($fh);
+	close($fh);
+    }
+}
+
+close($tty);

p.1

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+.Dd May 17, 2024
+.Dt TS 1
+.Os
+.Sh NAME
+.Nm p
+.Nd Paginate
+.Sh SYNOPSIS
+.Nm
+.Op Fl number
+.Ar
+.Sh DESCRIPTION
+.Nm
+copies its standard input, or the named files if given,
+to its standard output,
+stopping at the end of every page and at the end of each file.
+The special file name
+.Pa -
+can be used to refer explicitly to the standard input.
+.Pp
+Page size is defined by the
+.Ev LINES
+environment variable.
+If not defined, a default page size of 22 will be used.
+The page size can be overriden with the numeric option.
+.Pp
+While waiting for a newline,
+.Nm
+interprets the commands:
+.Bl -tag
+.It !
+Run the rest of the line as a shell command.
+.It q
+Quit.
+.El
+Any other input will show the next input page.
+.Sh ENVIRONMENT
+.Bl -tag -width LINES
+.It Ev LINES
+Number of lines of the terminal.
+.El
+.Sh EXIT STATUS
+.Ex -std
+.Sh HISTORY
+This is a reimplementation of Plan 9's
+.Nm
+pager.
+.Sh AUTHORS
+.An Adolfo Perez Alvarez Aq Mt adolfopa@sdf.org