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POPerl search and replace enters endless loop
 

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    <p>I am trying to match and replace in multiple files some string using</p> <pre><code>local $/; open(FILE, "&lt;error.c"); $document=&lt;FILE&gt;; close(FILE); $found=0; while($document=~s/([a-z_]+)\.h/$1_new\.h/gs){ $found=$found+1; }; open(FILE, "&gt;error.c"); print FILE "$document"; close(FILE);' </code></pre> <p>It enters an endless loop, because the result of the substitution is matched again by the regular expression searched for. But shouldn't this be avoided by the <code>s///g</code> construct?</p> <p><strong>EDIT:</strong></p> <p>I found that also a <code>foreach</code> loop will not do exactly what I want (it will replace all occurrences, but print only one of them). The reason seems to be that the perl substitution and and search behave quite differently in the <code>foreach()</code> and <code>while()</code> constructs. To have a solution to replace in multiple files which outputs also all individual replacements, I came up with the following <strong>body</strong>:</p> <pre><code># mandatory user inputs my @files; my $subs; my $regex; # additional user inputs my $fileregex = '.*'; my $retval = 0; my $opt_testonly=0; foreach my $file (@files){ print "FILE: $file\n"; if(not($file =~ /$fileregex/)){ print "filename does not match regular expression for filenames\n"; next; } # read file local $/; if(not(open(FILE, "&lt;$file"))){ print STDERR "ERROR: could not open file\n"; $retval = 1; next; }; my $string=&lt;FILE&gt;; close(FILE); my @locations_orig; my @matches_orig; my @results_orig; # find matches while ($string =~ /$regex/g) { push @locations_orig, [ $-[0], $+[0] ]; push @matches_orig, $&amp;; my $result = eval("\"$subs\""); push @results_orig, $result; print "MATCH: ".$&amp;." --&gt; ".$result." @[".$-[0].",".$+[0]."]\n"; } # reverse order my @locations = reverse(@locations_orig); my @matches = reverse(@matches_orig); my @results = reverse(@results_orig); # number of matches my $length=$#matches+1; my $count; # replace matches for($count=0;$count&lt;$length;$count=$count+1){ substr($string, $locations[$count][0], $locations[$count][1]-$locations[$count][0]) = $results[$count]; } # write file if(not($opt_testonly) and $length&gt;0){ open(FILE, "&gt;$file"); print FILE $string; close(FILE); } } exit $retval; </code></pre> <p>It first reads the file creates lists of the matches, their positions and the replacement text in each file (printing each match). Second it will replace all occurrences starting from the end of the string (in order not to change the position of previous messages). Finally, if matches were found, it writes the string back to the file. Can surely be more elegant, but it does what I want.</p>
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    1. CO... If I'm not mistaken, the `s///g` construct does *all* your replacements in one go, not one at a time. You shouldn't need a loop there at all. In other news: Why not `sed`?
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    2. COYes, you are absolutely right. The reason for the loop is that I want to count the number of matches as indicated (and possibly in future output what was matched). I do not use sed because I want exact perl syntax. The code will be part of a shell script.
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    3. COTo get the number of matches, you can do `$num_matches = ($data =~ s/([a-z_]+)\.h/$1_new\.h/g)`
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