I am having a string say
my $str = "FILLER-1-1,EQPT:MN,EQPT_MISSING,NSA,04-30,15-07-13,NEND,NA";
I want to match a pattern say
my $pattern = "FILLER-1-1";
I am using the below regexp
$reg = $str =~ /$pattern/;
This is working fine
Now the problem is it is also matching if our string is
FILLER-1-10/FILLER-1-11/FILLER-1-12 so on ...
I dont want to match this. Also I don't want my regexp to be like
$reg = $str =~ /$pattern\W+/;
This one is working against the above mentioned issue but \W may come or not come. In some strings it can come while in other it may not come. So i need the regexp to match only FILLER-1-1 without using \W+ and it should match specifically FILLER-1-10
Note: If somebody is doing -(minus) rating to my question, please let me know what's wrong in the code. It will be appreciable if the person write the comment too
As \w matches [a-zA-Z0-9], you can use the zero-width assumption \b, which denotes a change in \w state (called a "word boundary", hence the "b" shortcut):
/FILLER-1-1\b/
This means that there needs to be a character that differs from the previous word state - a word state change.
It will match
FILLER-1-1.
FILLER-1-1&
FILLER-1-1,
It will not match
FILLER-1-1a
FILLER-1-16
Read more about it here.
If you want to match FILLER at the start of the input (line) followed by two numbers, this simple regex should work:
/~FILLER-\d+-\d+/
~ matches the beginning of the input
\d matches any digit ([0-9])
+ matches at least one, but can match any number
use ? quantifier like so:
/FILLER-\d-\d\W?/
The \W? means not a word zero or one time
Related
Can someone help me understand why the following regex is matching when i would expect it not to match.
String to check against
/opt/lnpsite/ni00/flat/tmp/Med_Local_Bak/ROI_Med_Transfer/CBD99_PINPUK_14934_09_02_2017_12_07_36.txt
regex
(?<!Transfer\/)\w*PINPUK.*(?:csv|txt)$
I was expecting this to not match as the string Transfer/ appears before 0 or more word chars followed by the string PINPUK. If I change the pattern from \w* to \w{6} to explicitly match 6 word chars this correctly returns no match.
Can someone help me understand why with the 0 or more quantifier on my "word" character results in the regex giving a match?
Your regex pattern (?<!Transfer/)\w*PINPUK.*(?:csv|txt)$ is looking for \w*PINPUK not immediately preceded by Transfer/
Given the string
/opt/lnpsite/ni00/flat/tmp/Med_Local_Bak/ROI_Med_Transfer/CBD99_PINPUK_14934_09_02_2017_12_07_36.txt
the regex engine will start by matching \w*PINPUK with CBD99_PINPUK
But that is preceded by Transfer/ so the engine backtracks and finds BD99_PINPUK
That is preceded by C, which isn't Transfer/, so the match is successful
As for a fix, just put the slash outside the look-behind
(?<!Transfer)/\w*PINPUK.*(?:csv|txt)$
That forces the \w* to begin right after the slash, and the pattern now correctly fails
Borodin has given an excellent explanation of why this doesn't work and a solution for this case (move a /). Sometimes something simple like that isn't possible though so here I'll explain an alternate work around that might be useful
Things will match as you expect if you move the \w* inside the negative look-behind. Like so:
(?<!Transfer\/\w*)PINPUK.*(?:csv|txt)$
Unfortunately Perl doesn't allow this, negative look-behinds must be fixed width. But still, there is a way to perform one match: match in reverse
^(?:vsc|txt).*KUPNIP(?!\w*\/refsnarT)
This uses a variable length negative look-ahead, something Perl does allow. Putting all this together in a script we get
use strict;
use warnings;
use feature 'say';
my $string_matches = '/opt/lnpsite/ni00/flat/tmp/Med_Local_Bak/ROI_Med_Transfer/CBD99_PINPUK_14934_09_02_2017_12_07_36.txt';
say "Trying $string_matches";
if ( reverse($string_matches) =~ /^(?:vsc|txt).*KUPNIP(?!\w*\/refsnarT)/ ) {
say 'It matched';
} else {
say 'No match';
}
say '';
my $string_doesnt_match = '/opt/lnpsite/ni00/flat/tmp/Med_Local_Bak/ROI_Med/CBD99_PINPUK_14934_09_02_2017_12_07_36.txt';
say "Trying $string_doesnt_match";
if ( reverse($string_doesnt_match) =~ /^(?:vsc|txt).*KUPNIP(?!\w*\/refsnarT)/ ) {
say 'It matched';
} else {
say 'No match';
}
Which outputs
Trying /opt/lnpsite/ni00/flat/tmp/Med_Local_Bak/ROI_Med_Transfer/CBD99_PINPUK_14934_09_02_2017_12_07_36.txt
No match
Trying /opt/lnpsite/ni00/flat/tmp/Med_Local_Bak/ROI_Med/CBD99_PINPUK_14934_09_02_2017_12_07_36.txt
It matched
I need a perl regex to match A.CC3 on a line begining with something followed by anything then, my 'A.CC3 " and then anything...
I am surprised this (text =~ /^\W+\CC.*\A\.CC\[3].*/) is not working
Thanks
\A is an escape sequence that denotes beginning of line, or ^ like in the beginning of your regex. Remove the backslash to make it match a literal A.
Edit: You also seem to have \C in there. You should only use backslash to escape meta characters such as period ., or to create escape sequences, such as \Q .. \E.
At its simplest, a regex to match A.CC3 would be
$text =~ /A\.CC3/
That's all you need. This will match any string with A.CC3 in it. In the comments you mention the string you are matching is this:
my $text = "//%CC Unused Static Globals, A.CC3, Halstead Progam Volume";
You might want to avoid partial matches, in which case you can use word boundary \b
$text =~ /\bA\.CC3\b/
You might require that a line begins with //%
$text =~ m#^//%.*\bA\.CC3\b#
Of course, only you know which parts of the string should be matched and in what way. "Something followed by anything followed by A.CC3 followed by anything" really just needs the first simple regex.
It doesn't seem like you're trying to capture anything. If that's the case, and all you need to do is find lines that contain A.CC3 then you can simply do
if ( index( $str, 'A.CC3' ) >= 0 ) # Found it...
No need for a regex.
Try to give this a shot:
^.*?A\.CC.*$
That will match anything until it reaches A, then a literal ., followed by CC, then anything until end of string.
It depends what you want to match. If you want to pull back the whole line in which the A.CC3 pattern occurs then something like this should work:
^.*A\.CC3.*$
I am trying to craft a regular expression that will match all characters after (but not including) the first space in a string.
Input text:
foo bar bacon
Desired match:
bar bacon
The closest thing I've found so far is:
\s(.*)
However, this matches the first space in addition to "bar bacon", which is undesirable. Any help is appreciated.
You can use a positive lookbehind:
(?<=\s).*
(demo)
Although it looks like you've already put a capturing group around .* in your current regex, so you could just try grabbing that.
I'd prefer to use [[:blank:]] for it as it doesn't match newlines just in case we're targetting mutli's. And it's also compatible to those not supporting \s.
(?<=[[:blank:]]).*
You don't need look behind.
my $str = 'now is the time';
# Non-greedily match up to the first space, and then get everything after in a group.
$str =~ /^.*? +(.+)/;
my $right_of_space = $1; # Keep what is in the group in parens
print "[$right_of_space]\n";
You can also try this
(?s)(?<=\S*\s+).*
or
(?s)\S*\s+(.*)//group 1 has your match
With (?s) . would also match newlines
I want to know how pattern matching works in Perl.
My code is:
my $var = "VP KDC T. 20, pgcet. 5, Ch. 415, Refs %50 Annos";
if($var =~ m/(.*)\,(.*)/sgi)
{
print "$1\n$2";
}
I learnt that the first occurrence of comma should be matched. but here the last occurrence is being matched. The output I got is:
VP KDC T. 20, pgcet. 5, Ch. 415
Refs %50 Annos
Can someone please explain me how this matching works?
From docs:
By default, a quantified subpattern is "greedy", that is, it will match as many times as possible (given a particular starting location) while still allowing the rest of the pattern to match
So, first (.*) will take as much as possible.
Simple workaround is using non-greedy quantifier: *?. Or match not every character, but all except comma: ([^,]*).
Greedy and Ungreedy Matching
Perl regular expressions normally match the longest string possible.
For instance:
my($text) = "mississippi";
$text =~ m/(i.*s)/;
print $1 . "\n";
Run the preceding code, and here's what you get:
ississ
It matches the first i, the last s, and everything in between them. But what if you want to match the first i to the s most closely following it? Use this code:
my($text) = "mississippi";
$text =~ m/(i.*?s)/;
print $1 . "\n";
Now look what the code produces:
is
Clearly, the use of the question mark makes the match ungreedy. But theres another problem in that regular expressions always try to match as early as possible.
Source: http://www.troubleshooters.com/codecorn/littperl/perlreg.htm
Use question mark in your regex:
if($var =~ m/(.*?)\,(.*)/sgi)
{
print "$1\n$2";
}
So:
(.*)\, means: "match as much characters as you can as long as there will be a comma after them"
(.*?)\, means: "match any characters until you stumble upon a comma"
(.*)\, -you might expect that it will match till the first comma.
But it is greedy enough to match all the xcharacters it came across untill last comma instead of the first comma.
so
it matches till the last command.
and the second match is the rest of the line.
to avoid greedy pattern match adda ? after *
I need a little help with regex to match and replace
<comma|dash|fullstop|questionmark|exclamation mark|space|start-of-string>WORD<comma|dash|fullstop|space|end-of-string>
I need to find a specific WORD (case insensitive) which
is preceded by: comma or dash or fullstop or question mark or exclamation mark or space or start-of-string
and is followed by: comma or dash or fullstop or question mark or exclamation mark or space or end-of-string
test string:
MATCH me, yes please,MATCH me but dontMATCHme!MATCH me and of course MATCH, and finally MATCH
I want to REPLACE all matches with another string in PHP, so i possibly need to use preg_replace or something?
Try this
$input = "MATCH me, yes please,MATCH me but dontMATCHme!MATCH me and of course MATCH, and finally MATCH";
echo($input."<br/>");
$result = preg_replace("/
(?:^ # Match the start of the string
|(?<=[-,.?! ])) # OR look if there is one of these chars before
match # The searched word
(?=([-,.?! ]|$)) # look that one of those chars or the end of the line is following
/imx", # Case independent, multiline and extended
"WORD", $input);
echo($result);
This is not doing exactly what you asked for, but possibly fulfills your actual requirements better (which I'm guessing to be "Replace MATCH with WORD only if MATCH is an entire word, and not part of a different word"):
$input = 'MATCH me, yes please,MATCH me but dontMATCHme!MATCH me and of course MATCH, and finally MATCH'
$result = preg_replace('/\bMATCH\b/i', "WORD", $input)
The \b are word boundary anchors that only match at the start or end of an alphanumeric word.
Result:
WORD me, yes please,WORD me but dontMATCHme!WORD me and of course WORD, and finally WORD
Here is an implementation in PHP that will do the task you described. It will replace all words with "WORD".
<?php
$msg = "MATCH me, yes please,MATCH me but dontMATCHme!MATCH me and of course MATCH, and finally MATCH";
echo($msg."<br/><br/>");
$msg = preg_replace("/(\w)+/", "WORD", $msg);
echo($msg."<br/>");
?>