If you want to change the string in place, you can use s///ge: 
use warnings;
use strict;

my $content = '{ "geometry": { "type": "Polygon", "coordinates": [ [ [
+ 19.054804912278406, 47.485785556135411 ], [ 19.057857836771483, 47.4
+87322542030711 ], [ 19.06025597925397, 47.488491565765209 ], [ 19.060
+347248086835, 47.488539642204628 ], [ 19.060463310421543, 47.48457828
+7406251 ], [ 19.054804912278406, 47.485785556135411 ] ] ] } }';

$content =~ s/(\d\d\.\d*)/substr($1,0,9)/ge;
print "$content\n";

__END__

{ "geometry": { "type": "Polygon", "coordinates": [ [ [ 19.054804, 47.
+485785 ], [ 19.057857, 47.487322 ], [ 19.060255, 47.488491 ], [ 19.06
+0347, 47.488539 ], [ 19.060463, 47.484578 ], [ 19.054804, 47.485785 ]
+ ] ] } }

[download]

In reply to Re: In-place regex substitution by toolic
in thread In-place regex substitution by lmocsi

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.