Try

$string =~ s/^(.{0,$maxlength})\b.*$/$1.../s;
[download]

Edit: explanation: you can ommit the upper bound, but not the lower bound, as you did. From perlre:

     {n}?   Match exactly n times
     {n,}?  Match at least n times
     {n,m}? Match at least n but not more than m times
[download]

Darn it, I swear I remember being able to omit the minimum number of matches. I wonder what it was doing with my regular expression since it didn't issue a warning. Thanks for pointing out the other error, too, I hadn't even thought about that yet.

What about the standard module Text:: Wrap?

Here's a promising-sounding snippet from its docs:

Text::Wrap::wrap() is a very simple paragraph formatter. It formats a single paragraph at a time by breaking lines at word boundaries.

Or if that's not sufficient, Text::Autoformat is capable of more complex things.

Maybe I read it wrong, but it looks like those modules are geared toward displaying all the text, just divided into lines. I wanted to only display the first part, kind of like a preview.

Try Text::Autformat and split to get the first line.

use strict;
use warnings;

use Text::Autoformat;

my $string = 'A lengthy text with more than xxx characters to demonstr
+ate truncate';


print "Before: $string\n";
print 'Length: ' , length($string) , "\n";

my $truncated  = &truncate($string,20);


print "After: $truncated\n";
print 'Length: ' , length($truncated) , "\n";

###########################################################
sub truncate {
    my $string = shift @_;
    my $length = 75; 
    $length = shift if @_;
    

    $string = autoformat($string, {     left  => 0,
                                      right => $length ,
                                      widow => 0,
                                 });
        ($string) = split(/\n/,$string); # Just the first element
        
        return $string;
} ##
###########################################################
[download]

Just my two cents. Hope this helps

1. Does your string contain a space in the first N characters? If not, abort.
2. Truncate at N+1 characters
3. Truncate at last space or in string (use the rindex function)

sub truncate_string {
  my($string, $maxlength) = @_;
  $string = substr($string, 0, $maxlength+1);
  die("Can't truncate, no spaces\n") if(index($string, ' ') == -1);
  return substr($string, 0, rindex($string, ' ') - 1);
}
[download]

You needn't cut it if the string is not longer than maxlength. Just return the original string then.

return substr($string, 0, rindex($string, ' ') - 1);

I'd cut it on any whitespace, or at least, in front of the last partial word, like this:

$string =~ s/\s*[\w\-]*$/.../;
return $string;
[download]

I'm assuming that a hyphen is a part of a word. Your idea may differ from mine.

p.s. Hmm, that'll leave any trailing nonword/nonspace characters, for example punctuation characters, intact, making the string just one character too long.

Perhaps this is better?

$string =~ s/\s*(?:[\w\-]+|\W)$/.../;
[download]

or

$string =~ s/\s*[\w\-]+$/.../ or $string =~ s/\s*\W$/.../;
[download]

Assuming you're working on a paragraph of text and want to also break within words. If that's not what you meant with your OP, this probably isn't what you're looking for.

Doing a quick CPAN search, would Tex::Hyphen be something for you? From the list of changes, it would also seem to support other languages than English.

sub truncate_string($$) {
    my ( $string, $max ) = @_;

    # always do nothing if already short enough 
    ( length( $string ) <= $max ) and return $string;

    # issue warning if forced to chop a word anyway
    if ( $string =~ /\s/ ) {
        warn "cannot truncate string on word boundary";
        return substr( $string, 0, $max );
    }

    # truncate pre-existing trailing whitespace
    $string =~ /^(.*)\s+$/ and return $1;

    # otherwise truncate on word boundary 
    $string =~ s/\S+$// and return $string;
    
    die; # unreachable
}
[download]