These two subs emulate the 'show all characters' functionality of most good text editors. Tabs are changed to ' -> ' and spaces to dots '·' (chr 183 ASCII). The funny backwards P symbol '¶' (chr 182 ASCII) is used for newlines. We use the octal naming convention for these chars for convenience. chr 0266 = '¶' and chr 0267 = '·'

In the unlikely event these special chars are included in the text to be processed we hex encode them using the standard URL encoding convention of a % followed by two hex digits. We can then remove the URL encoding to regenerate our original text.

The output of the show sub is shown in the second 4 lines of data which were the output on the first 4 lines. They provide the test case for the encoding.

Efficiency hacks courtesty bbfu and Hofmator.

sub show {
    my @data = @_;
    for (@data) {
        s/\266/%B6/g;
        s/\267/%B7/g;
        tr/ /\267/;
        s/\t/ -> /g;
        s/\n/\266\n/g;
    }
  return wantarray ? @data : join'',@data;
}

sub hide {
    my @data = @_;
    for (@data) {
        s/ -> /\t/g;
        tr/\266//d;
        tr/\267/ /;
        s/%B6/\266/g;
        s/%B7/\267/g;
    }
  return wantarray ? @data : join'',@data;
}

@data = (<DATA>)[0..7];

print "Original data, including specials\n\n";
print @data;

print "\n\nShow invisible chars in data\n\n";
print show(@data);

print "\n\nHide and show data - should not change\n\n";
print hide(show(@data));

__DATA__
    tab
    4 spaces, trailing tab    
        tab and 4 spaces
        
 -> tab¶
····4·spaces,·trailing·tab -> ¶
 -> ····tab·and·4·spaces¶
 ->  -> ¶
¶

[download]

In reply to Show All Characters in Text by tachyon

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.