Suppose there is a text like this:
|-SAMPLE-D2
|---SAMPLE-D1
|---SAMPLE3
I want to count the number of "-" after |.
I tried to parse that by using the following regular expression in perl
$count=()= /-/g;
but this is problematic because the first two has "-" somewhere else in the text as well as in the front. How should I form my regex or use other function in perl to get the number of "-" right after "|"?
Regex to match the dashes after the starting |:
/^\|([\-]*)/
To count dashes that are not preceded by a letter, use a negative look-behind assertion.
$count = () = /(?<!\w)-/g
If the vertical line only ever comes at the start you can get the string of repeating minuses with:
my ($match) = $txt =~ /^\|(-*)/;
The brackets around $match cause the captured portion of the regex to be put into it
then get the number of minuses using
my $minus_count = length($match || '');
The
|| '')
bit
Initialises $match if the regex above found no matches at all, to stop length moaning about uninitialised variables (if you have warnings on)
Not sure if you can count in Regex directly but you can extract capture groups and do a simple arithmetic with their string lengths:
#!/usr/bin/perl
use warnings;
my $inFile = $ARGV[0];
open(FILEHANDLE, "<", $inFile) || die("Could not open file ".$inFile);
my #fileLines = <FILEHANDLE>;
my $lineNo = 0;
my $rslt;
foreach my $line(#fileLines) {
chomp($line);
$line =~ s/^\s+//;
$line =~ s/\s+$//;
$lineNo++;
print "\n".$lineNo." = <".$line.">";
if($line =~ m/^\|-+(.+)/) {
my $text = $1;
print "\n\ttext = <".$text.">";
my $minCnt = length($line) - length($text) - 1;
print "\n\tminus count = <".$minCnt.">";
}
}
close(FILEHANDLE);
Related
I'm trying to extract text and numbers from a string using regex in perl. Here is my code:
$line = "finish=100\n";
($var) = $line =~ /[a-z]+/;
($val) = $line =~ /[0-9]+/;
My expected output is that $var = "finish" and $val = 100. However when I run the code $var = 1 and $val = 1.
Any help would be appreciated!!
Use capturing parentheses inside your regular expressions:
$line = "finish=100\n";
($var) = $line =~ /([a-z]+)/;
($val) = $line =~ /([0-9]+)/;
print "$var $val\n";
Refer to perlre
A regex match in list context (where the regex doesn't use the /g flag) returns
the empty list if it fails
a list of captured substrings ($1, $2, ...) if it succeeds and the pattern contains capturing groups
the list 1 if it succeeds and the pattern doesn't capture anything
Your regexes match, but they don't contain any capturing groups, so that's why you get 1 in $var and $val.
If you add capturing groups (/([a-z]+)/, /([0-9]+)/), you get the matched substrings instead.
Note that it might be easier to just do it all in one match:
my ($var, $val) = $line =~ /^([a-z]+)=([0-9]+)$/;
This way you also validate that the input string has the expected form and isn't just something like "Cat o' 9 tails", which (with your original regexes) would extract $var = "at" and $val = "9".
You can too get two values in one array, maybe with this:
$line = "finish=100\n";
#matches = $line =~ /(\w+)\W(\d+)/;
print "$matches[0], $matches[1]";
The following perl program has a regex written to serve my purpose. But, this captures results present within a string too. How can I only get strings separated by spaces/newlines/tabs?
The test data I used is present below:
http://sainikhil.me/stackoverflow/dictionaryWords.txt
use strict;
use warnings;
sub print_a_b {
my $file = shift;
$pattern = qr/(a|b|A|B)\S*(a|b|A|B)/;
open my $fp, $file;
my $cnt = 0;
while(my $line = <$fp>) {
if($line =~ $pattern) {
print $line;
$cnt = $cnt+1;
}
}
print $cnt;
}
print_a_b #ARGV;
You could consider using an anchor like \b: word boundary
That would help apply the regexp only after and before a word.
\b(a|b|A|B)\S*(a|b|A|B)\b
Simpler, as Avinash Raj adds in the comments:
(?i)\b[ab]\S*[ab]\b
(using the case insensitive flag or modifier)
If you have multiple words in the same line then you can use word boundaries in a regex like this:
(?i)\b[ab][a-z]*[ab]\b
The pattern code is:
$pattern = /\b[ab][a-z]*[ab]\b/i;
However, if you want to check for lines with only has a word, then you can use:
(?i)$[ab][a-z]*[ab]$
Update: for your comment * lines that begin and end with the same character*, you can use this regex:
(?i)\b([a-z])[a-z]*\1\b
But if you want any character and not letters only like above you can use:
(?i)\b(.)[a-z]*\1\b
How can I extract string after a symbol in Perl?
I tried doing some searches but even the code I found didn't work.
I'm trying to extract the string after a colon. So I want to show everything after the colon.
Example:
string = day1: string over here
substring = string over here
So far I have tried:
$substring = $string=~ /(\:.*)\s*$/;
But it only outputs the number 1 over and over.
That's because pattern matches in a scalar context are boolean tests. If you want to capture bracket content (capture groups), you need a list context. It's ok if the list is only one element though:
try this:
my ( $substring ) = $string=~ /(\:.*)\s*$/;
Difference maybe a bit subtle, but basically - we are assigning 'all the hits' from the pattern match to a list... that comprises one element.
Note - that's so you can do:
my #matches = $string =~ m/(.)/g;
And get multiple 'hits' returned. If you do as above, you will only get the first match - which is irrelevant given your pattern, but you can do:
my ( $key, $value ) = $string =~ m/(\w+)=(\w+)/;
for example.
I usually use parentheses to extract a part from text and then refer to the result stored in $1 variable.
look at example:
my $text = "day1: string over here";
print $1 if ($text =~ /:\s*(.+)$/);
but similar result may be recieved with this code too:
my $text = "day1: string over here";
my ($a) = $text =~ /:\s*(.+)$/;
print $a;
You can achieve desire substring by using split function also:
#!/usr/bin/perl
use warnings;
use strict;
my $string = "day1: string over here";
my (undef, $substring) = split(':\s*', $string);
print $substring, "\n";
Output:
string over here
Or you can get this by using capturing group () in regex:
my $string = "day1: string over here";
$string =~ m/(.*)\:\s+(.*)$/;
my $substring = $2;
print $substring, "\n";
I have a file containing regular expressions, e.g.:
City of (.*)
(.*) State
Now I want to read these (line by line), match them against a string, and print out the extraction (matched group). For example: The string City of Berlin should match with the first expression City of (.*) from the file, after that Berlin should be extracted.
This is what I've got so far:
use warnings;
use strict;
my #pattern;
open(FILE, "<pattern.txt"); # open the file described above
while (my $line = <FILE>) {
push #pattern, $line; # store it inside the #pattern variable
}
close(FILE);
my $exampleString = "City of Berlin"; # line that should be matched and
# Berlin should be extracted
foreach my $p (#pattern) { # try each pattern
if (my ($match) = $exampleString =~ /$p/) {
print "$match";
}
}
I want Berlin to be printed.
What happens with the regex inside the foreach loop?
Is it not compiled? Why?
Is there even a better way to do this?
Your patterns contain a newline character which you need to chomp:
while (my $line = <FILE>) {
chomp $line;
push #pattern, $line;
}
First off - chomp is the root of your problem.
However secondly - your code is also very inefficient. Rather than checking patterns in a foreach loop, consider instead compiling a regex in advance:
#!/usr/bin/env perl
use strict;
use warnings;
# open ( my $pattern_fh, '<', "pattern.txt" ) or die $!;
my #patterns = <DATA>;
chomp(#patterns);
my $regex = join( '|', #patterns );
$regex = qr/(?:$regex)/;
print "Using regex of: $regex\n";
my $example_str = 'City of Berlin';
if ( my ($match) = $example_str =~ m/$regex/ ) {
print "Matched: $match\n";
}
Why is this better? Well, because it scales more efficiently. With your original algorithm - if I have 100 lines in the patterns file, and 100 lines to check as example str, it means making 10,000 comparisons.
With a single regex, you're making one comparison on each line.
Note - normally you'd use quotemeta when reading in regular expressions, which will escape 'meta' characters. We don't want to do this in this case.
If you're looking for even more concise, you can use map to avoid needing an intermediate array:
my $regex = join( '|', map { chomp; $_ } <$pattern_fh> );
$regex = qr/(?:$regex)/;
print "Using regex of: $regex\n";
my $example_str = 'City of Berlin';
if ( my ($match) = $example_str =~ m/$regex/ ) {
print "Matched: $match\n";
}
How do you create a $scalar from the result of a regex match?
Is there any way that once the script has matched the regex that it can be assigned to a variable so it can be used later on, outside of the block.
IE. If $regex_result = blah blah then do something.
I understand that I should make the regex as non-greedy as possible.
#!/usr/bin/perl
use strict;
use warnings;
# use diagnostics;
use Win32::OLE;
use Win32::OLE::Const 'Microsoft Outlook';
my #Qmail;
my $regex = "^\\s\*owner \#";
my $sentence = $regex =~ "/^\\s\*owner \#/";
my $outlook = Win32::OLE->new('Outlook.Application')
or warn "Failed Opening Outlook.";
my $namespace = $outlook->GetNamespace("MAPI");
my $folder = $namespace->Folders("test")->Folders("Inbox");
my $items = $folder->Items;
foreach my $msg ( $items->in ) {
if ( $msg->{Subject} =~ m/^(.*test alert) / ) {
my $name = $1;
print " processing Email for $name \n";
push #Qmail, $msg->{Body};
}
}
for(#Qmail) {
next unless /$regex|^\s*description/i;
print; # prints what i want ie lines that start with owner and description
}
print $sentence; # prints ^\\s\*offense \ # not lines that start with owner.
One way is to verify a match occurred.
use strict;
use warnings;
my $str = "hello what world";
my $match = 'no match found';
my $what = 'no what found';
if ( $str =~ /hello (what) world/ )
{
$match = $&;
$what = $1;
}
print '$match = ', $match, "\n";
print '$what = ', $what, "\n";
Use Below Perl variables to meet your requirements -
$` = The string preceding whatever was matched by the last pattern match, not counting patterns matched in nested blocks that have been exited already.
$& = Contains the string matched by the last pattern match
$' = The string following whatever was matched by the last pattern match, not counting patterns matched in nested blockes that have been exited already. For example:
$_ = 'abcdefghi';
/def/;
print "$`:$&:$'\n"; # prints abc:def:ghi
The match of a regex is stored in special variables (as well as some more readable variables if you specify the regex to do so and use the /p flag).
For the whole last match you're looking at the $MATCH (or $& for short) variable. This is covered in the manual page perlvar.
So say you wanted to store your last for loop's matches in an array called #matches, you could write the loop (and for some reason I think you meant it to be a foreach loop) as:
my #matches = ();
foreach (#Qmail) {
next unless /$regex|^\s*description/i;
push #matches_in_qmail $MATCH
print;
}
I think you have a problem in your code. I'm not sure of the original intention but looking at these lines:
my $regex = "^\\s\*owner \#";
my $sentence = $regex =~ "/^\s*owner #/";
I'll step through that as:
Assign $regexto the string ^\s*owner #.
Assign $sentence to value of running a match within $regex with the regular expression /^s*owner $/ (which won't match, if it did $sentence will be 1 but since it didn't it's false).
I think. I'm actually not exactly certain what that line will do or was meant to do.
I'm not quite sure what part of the match you want: the captures, or something else. I've written Regexp::Result which you can use to grab all the captures etc. on a successful match, and Regexp::Flow to grab multiple results (including success statuses). If you just want numbered captures, you can also use Data::Munge
You can do the following:
my $str ="hello world";
my ($hello, $world) = $str =~ /(hello)|(what)/;
say "[$_]" for($hello,$world);
As you see $hello contains "hello".
If you have older perl on your system like me, perl 5.18 or earlier, and you use $ $& $' like codequestor's answer above, it will slow down your program.
Instead, you can use your regex pattern with the modifier /p, and then check these 3 variables: ${^PREMATCH}, ${^MATCH}, and ${^POSTMATCH} for your matching results.