Q: is there a processor saving in using substr rather than a regex?

In general yes, but not if you have to combine the substr with a regex (as MZSanford does here).

The benchmark shows that the pure regex approach suggested by tye is quickest for your problem, closely followed by japhy's version using fancier regex constructs. MZSanford's substr/substitute is slow (and a bit buggy, fixed that below :) because it tries to start the match at every interior whitespace. But you can improve on it: ($chunk) = substr($string,0,201) =~ /(.*)\s+\w*$/',

Here are the results of the benchmark: 

Benchmark: running Hofmator, MZSanford, japhy, tye, each for at least 
+3 CPU seconds...
  Hofmator:  3 wallclock secs ( 2.99 usr +  0.01 sys =  3.00 CPU) @ 20
+6100.67/s (n=618302)
 MZSanford:  4 wallclock secs ( 3.03 usr +  0.00 sys =  3.03 CPU) @ 55
+936.63/s (n=169488)
     japhy:  4 wallclock secs ( 3.00 usr +  0.00 sys =  3.00 CPU) @ 25
+6036.67/s (n=768110)
       tye:  4 wallclock secs ( 3.00 usr +  0.00 sys =  3.00 CPU) @ 29
+2146.67/s (n=876440)

[download]

generated by this code: 

#!/usr/bin/perl
use Benchmark qw/timethese/;
 
$string = q/Some text repeated / x 50;

timethese(-3, {
    MZSanford => '$chunk = substr($string,0,201);$chunk =~ s/\s+\w*$//
+',
    Hofmator  => '($chunk) = substr($string,0,201) =~ /(.*)\s+\w*$/',
    japhy     => '($chunk) = $string =~ /^(.{1,200})(?<!\s)(?!\w)/;',
    tye       => '($chunk) = $string =~ /^(.{0,199}\S)\s/',
});

[download]

-- Hofmator

In reply to Re3: Regex: get first N characters but break at whitespace by Hofmator
in thread Regex: get first N characters but break at whitespace by George_Sherston

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.