See sample code below
> Chaps,
>
> Please i need help on the regular expression, i have the sample code
> below.
> I only want to match the entries from the array to the file and print
> the
> matching line
>
> for example if i only want to match fc3/23, in my code it prints both
> the
> lines fc3/2 and fc3/23. How to restrict to exact matches and print
> only ex:
> fc3/23
>
>
>
> out.txt
> ------
>
> fc3/2 10:00:00:00 host1
> fc3/23 10:00:00:00 host2
> fc10/1 10:00:00:00 host3
> fc10/11 10:00:00:00 host4
> fc3/1 10:00:00:00 host5
> fc3/14 10:00:00:00 host6
> fc12/1 10:00:00:00 host7
> fc12/12 10:00:00:00 host8
>
>
> sample code
> -----------------
>
> my @check = (fc3/23, fc10/1, fc3/14, fc12/12);
>
> my $f2 = 'out.txt';
> for my $element(@check) {
> open my $fh2, '<', $f2 or die "could not open $f2: $!";
> while (my $line = <$fh2>) {
> chomp $line;
> if ($line = / ^(fc\d+\/\d+/) {
> $match=$&;
> }
> if ($element =~ $match) {
> print "$line \n";
> }
> }
> }
>
>
> required output
> --------------------
>
> fc3/23 10:00:0:00 host2
> fc10/1 10:00:0:00 host3
> fc3/14 10:00:00:00 host6
> fc12/12 10:00:00:00 host8
>
> Thanks
> Sj
>
This worked for me:
#!/usr/bin/perl
use strict; # Always a good idea!
use warnings; # likewise!
# You need quotes around your literals in the line that creates
# and assigns @check:
my @check = ("fc3/23", "fc10/1", "fc3/14", "fc12/12");
my $f2 = 'out.txt';
# The following lines create a reqexp variable that will match any
# of the strings in @check. Note in the map that I placed a space
# after "$_". This takes care of the problem where "fc3/2" matched
# "fc3/23". When this is done, for this sample, the generated regular
# expression looks like:
# (?:fc3/23 )|(?:fc10/1 )|(?:fc3/14 )|(?:fc12/12 )
# This attempts to match against all of the strings that were in
@check.
# The use of "(?:" instead of "(" to start each group will make the
# parenthesis "non-capturing", which is a bit quicker when you don't
need
# to capture the actual matches.
#
my @tmpcheck = map {"(?:$_ )"} @check;
my $regexp_str = join "|", @tmpcheck;
my $regexp = qr/$regexp_str/;
open my $fh2, '<', $f2 or die "could not open $f2: $!";
while (my $line = <$fh2>) {
print "$line" if $line =~ $regexp; # Print only lines that match
}
# Note that I did not chomp the newline and put it back on when
printing.
# The presence of the newline does not effect the match in this
case, so
# that was not necessary.
Best of luck.
Nathan
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