Match file names in if condition of perl - perl

Question

I've files with filenames such as lin.txt and lin1.txt along with other .txt files. I need to find only these files and print its content only by one. I've the below code, but its somehow not matching the files starting with lin*. What is the issue?
$te_dir= "/projects/xxx/";
opendir (DIR, $te_dir) or die $!;
while (my $file = readdir(DIR))
{
if ($file=~/\.txt/)
{
#// Doing some tasks.
if($file ~= 'lin*.txt')
{
$linfile=$te_dir/$file;
open(LINFILE, $linfile) or die "Couldn't open file $file:$!";
while(my $line = <LINFILE>)
{
print $line;
}
close LINFILE;
}
}
}

Answer 1

You are mixing globs (shell wildcards) with regular expressions. These are two different formalisms with different syntax and semantics. In regular expressions (which is what Perl matching uses), n* matches zero or more occurrences of the character n. You probably mean
if ($file =~ /lin.*\.txt/)
Notice also the syntax error in the operator. You correctly have =~ in the first conditional, but you misspelled it as ~= where you do this comparison. (Maybe it's just a transcription error; for me, this creates a clear syntax error, so the script would not run in the first place.)
As noted in #brianadams' answer, the proper regular expression for this is
if ($file =~ /^lin.*\.txt$/)
with beginning of line ^ and end of line $ anchors to prevent e.g. feline.txt.html from matching. The default behavior of Perl's regular expressions is to find a match anywhere in the input string.

Answer 2

Here's a quick (and minimal) rewrite of your code that might help:
use strict;
use warnings;
my $te_dir = "/projects/xxx/";
opendir( my $dirh, $te_dir ) or die "Could not open '$te_dir': $!";
while ( my $file = readdir($dirh) ) {
next unless $file =~ /\.txt$/;
#// Doing some tasks.
if ( $file =~ /^ lin \d* \.txt $/x ) {
my $linfile = "$te_dir/$file";
open( my $fh, $linfile ) or die "Couldn't open file $linfile: $!";
while ( my $line = <$fh> ) {
print $line;
}
close $fh or die "Could not close $linfile: $!";
}
}
First, note that we've put strict and warnings at the top of the code. That will tell you about all sorts of interesting issues, including misspelled variable names.
Next, we've switch to lexical handles (e.g., my $dirh instead of DIR). The "bareword" version of the handles you're using (DIR and LINFILE have been discouraged for a long time because those are effectively global constructs and generally global data is bad because when it gets broken, it's awfully hard to tell what broke it, so we much, much prefer the lexical versions (the handles declared with the my builtin).
Also, this line you had probably doesn't do what you're thinking:
$linfile=$te_dir/$file;
You're trying to smash together a directory and filename with a forward slash, but since you didn't use string interpolation, you're actually using division. Both your director and filename will, in this numeric context, probably evaluate to zero, giving you a divide by zero error when you're trying to open a file!
However, if you're willing to use a CPAN module, you can make this even easier:
use strict;
use warnings;
use File::Find::Rule;
my $te_dir = "/projects/xxx/";
my #files = File::Find::Rule->file->name('lin*.txt')->in($te_dir);
foreach my $linfile (#files) {
#// Doing some tasks.
open my $fh, $linfile or die "Couldn't open file $linfile: $!";
while ( my $line = <$fh> ) {
print $line;
}
}
No muss, no fuss. Get only the files you want in the first pass and already have the correct file names (note that I didn't close the filehandle because it will close automatically when $fh goes out of scope at the end of the foreach loop.)

Answer 3

To match files starting with lin
if ( $file =~ /^lin.*\.txt$/ )

Answer 4

Try changing your 2nd if condition from this,
if($file ~= 'lin*.txt')
to this,
if($file =~ /lin*\.txt/)
You could also try: if($file =~ /^lin*\.txt/) , as already pointed out in other answers, but you'll need to make sure that the file names stored in the $file variable contain only the file name and not the entire path as well.