Perl Cookbook

Editing Input

Problem

You want a user to be able to edit a line before sending it to you for reading.

Solution

Use the standard Term::ReadLine library along with the Term::ReadLine::Gnu module from CPAN:

use Term::ReadLine;

$term = Term::ReadLine->new("APP DESCRIPTION");
$OUT = $term->OUT || *STDOUT;

$term->addhistory($fake_line);
$line = $term->readline(PROMPT);

print $OUT "Any program output\n";

Discussion

The program in Example 15.4 acts as a crude shell. It reads a line and passes it to the shell to execute. The readline method reads a line from the terminal, with editing and history recall. It automatically adds the user’s line to the history.

Example 15-4. vbsh

#!/usr/bin/perl -w
# vbsh -  very bad shell
use strict;

use Term::ReadLine;
use POSIX qw(:sys_wait_h);

my $term = Term::ReadLine->new("Simple Shell");
my $OUT = $term->OUT() || *STDOUT;
my $cmd;

while (defined ($cmd = $term->readline('$ ') )) {
    my @output = `$cmd`;
    my $exit_value  = $? >> 8;
    my $signal_num  = $? & 127;
    my $dumped_core = $? & 128;
    printf $OUT "Program terminated with status %d from signal %d%s\n",
           $exit_value, $signal_num, 
           $dumped_core ? " (core dumped)" : "";
    print @output;
    $term->addhistory($cmd);
}

If you want to seed the history with your own functions, use the addhistory method:

$term->addhistory($seed_line);

You can’t seed with more than one line at a time. To remove a line from the history, use the remove_history method, which takes an index into the history list. 0 is the first (least recent) entry, ...