Check is not happening please let me know where is the mistake. 
open FILE,"config.txt" or die "cannot open file : $!";
my $interface; # declare the variable
while(<FILE>) {
 if (/Link encap/){
 # if there are non-space symbols on the start of the line,
 # consider it interface name
 $interface = $1 if /^([\S]+)/; # $1 means first matched () group of s
+ymbols
 # a group of numeric symbols or dots after "inet addr:"
 # is considered an IP-address
 print "$interface => $1\n" if /inet addr:([0-9.]+)/;
 # use /inet6? addr: ?([0-9a-f.]+)/ if you want to match IPv6-addresse
+s
}
print;
}

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In reply to Re^8: need to remove the extra line in regular expression by laksh
in thread need to remove the extra line in regular expression by ulaksh

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