in reply to Regex: negative look ahead

If the goal here is to do things with strings which do not match a pattern, don't try to use a negative look-ahead -- just negate the test:

my @strings = (
    "ERROR blah license will expire",
    "ERROR blah something else",
    "ERROR blah Error processing Cancel Execution",
);
foreach (@strings) {
    if (!($_ =~ /^ERROR.+?(Error processing Cancel Execution|license w
+ill expire)$/)) {
      print "Do something with '$_'\n";
    }
}

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Re^2: Regex: negative look ahead
by johngg (Canon) on Apr 10, 2012 at 12:43 UTC

    Note that

    if ( ! ( $string =~ /pattern/ ) ) {

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    can be written

    if ( $string !~ /pattern/ ) {

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    I hope this is of interest.

    Cheers,

    JohnGG

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Re^2: Regex: negative look ahead
by fcaw1 (Initiate) on Apr 10, 2012 at 12:32 UTC
    Hi there I am writing a script with tails a log file and for each line runs multiple regular expressions against it (which are contained in a config file). Below are some examples of the log lines 
    ERROR 2012-04-02 05:00:18 Error processing Cancel Execution '2012-CSNY
+1CMR-1-20120402-1247 52938803o122h090000507' with LHDRSeqId 'CSNY1CMR
+1-1333315812780-2759'.

[2012-04-02 07:04:27,275][ERROR][101574:Company:japan][analytics.bond.
+BondAlibImpl] ALIB license will expire in29 days. Please upgrade lice
+nse file under /app/license

2012-04-02 05:00:18,810[ERROR] limitCheck: error while checking instru
+ction xxx.core.biz.order.instruction.EquityOrderSubmitInstruction(tsI
+d=20120402-090237887-340-509,order=20120402-090237880-767-508:TS)

    [download]

    With my original regular expression I would want to ignore the first two lines but match the third line. Thanks!

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[d/l]

      It could be a good idea to split the big regex.

      A good example: if you want to match lines with the words 'red' and 'dog'.

      The first idea is often to write something like: $line =~ /red.*dog|dog.*red/

      but there is a better way: $line=~/dog/ and $line=~/red/

      So, it's probably better to treat each exclusion with one regex:  next if /regex/;

      while (my $line = <DATA>) {
    next if $line =~ /^ERROR.*?Error processing Cancel Execution/;
    next if $line =~ /ERROR.*?license will expire/;
    print "Do something with the line: $line";
}
__DATA__
ERROR 2012-04-02 05:00:18 Error processing Cancel Execution '2012-CSNY
+1CMR-1-20120402-1247 52938803o122h090000507' with LHDRSeqId 'CSNY1CMR
+1-1333315812780-2759'.
[2012-04-02 07:04:27,275][ERROR][101574:Company:japan][analytics.bond.
+BondAlibImpl] ALIB license will expire in29 days. Please upgrade lice
+nse file under /app/license
2012-04-02 05:00:18,810[ERROR] limitCheck: error while checking instru
+ction xxx.core.biz.order.instruction.EquityOrderSubmitInstruction(tsI
+d=20120402-090237887-340-509,order=20120402-090237880-767-508:TS)

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