Text::Conceal - conceal and recover interface for text processing


    use Text::Conceal;
    my $conceal = Text::Conceal->new(
        length => \&sub,
        match  => qr/regex/,
    $_ = foo(@args);


Version 1.01


This is a general interface to transform text data into desirable form, and recover the result after the process.

For example, Text::Tabs does not take care of Asian wide characters to calculate string width. So next program does not work as we wish.

    use Text::Tabs;
    print expand <>;

In this case, make conceal object with length function which can correctly handle wide character width, and the pattern of string to be concealed.

    use Text::Conceal;
    use Text::VisualWidth::PP;
    my $conceal = Text::Conceal->new(
        length => \&Text::VisualWidth::PP::width,
        match  => qr/\P{ASCII}+/,

Then next program encode data, call expand() function, and recover the result into original text.

    my @lines = <>;
    my @expanded = expand @lines;
    print @expanded;

Be aware that encode and decode method alter the values of given arguments. Because they return results as a list too, this can be done more simply.

    print $conceal->decode(expand($conceal->encode(<>)));

Next program implements ANSI terminal sequence aware expand command.

    use Text::ANSI::Fold::Util qw(ansi_width);

    my $conceal = Text::Conceal->new(
        length => \&ansi_width,
        match  => qr/[^\t\n]+/,
    while (<>) {
        print $conceal->decode(expand($conceal->encode($_)));

Calling decode method with many arguments is not a good idea, since replacement cycle is performed against all entries. So collect them into single chunk if possible.

    print $conceal->decode(join '', @expanded);



Create conceal object. Takes following parameters.

length => function

Function to calculate text width. Default is length.

match => regex

Specify text area to be replaced. Default is qr/.+/s.

max => number

When the maximum number of replacement is known, give it by max parameter to avoid unnecessary work.

test => regex or sub

Specify regex or subroutine to test if the argument is to be processed or not. Default is undef, and all arguments will be subject to replace.

except => string

Text concealing is done by replacing text with different string which can not be found in any arguments. This parameter gives additional string which also to be taken care of.

visible => number

With default value 0, this module uses characters in the range:

    [0x01 => 0x07], [0x10 => 0x1f], [0x21 => 0x7e], [0x81 => 0xfe]

Use printable characters first, then use non-printable characters.

    [0x21 => 0x7e], [0x01 => 0x07], [0x10 => 0x1f], [0x81 => 0xfe]

Use only printable characters.

    [0x21 => 0x7e]

Encode/Decode arguments and return them. Given arguments will be altered.


All arguments given to encode method have to appear in the same order in the pre-decode string. Each argument can be shorter than the original, or it can even disappear.

If an argument is trimmed down to single byte in a result, and it have to be recovered to wide character, it is replaced by single space.

Replacement string is made of characters those are not found in any arguments. So if they contains all characters in the given range, encode stop to work. It requires at least two.

Minimum two characters are enough to produce correct result if all arguments will appear in the same order. However, if even single item is missing, it won't work correctly. Using three characters, one continuous missing is allowed. Less characters, more confusion.



This module is originally implemented as a part of Text::VisualPrintf module.



Kazumasa Utashiro


Copyright 2020-2022 Kazumasa Utashiro.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.