Multiple files opened

kokakola613 has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I'm trying to write a script that parses a file, which itself contains file names. I want to open each one of these files listed and perform some data analysis. However, I'm getting an error any way I try to do it.

Here is my original code (adapted)


open(INP, "<$file_list") or die("Error reading file");
while (<INP>) {
   my $data_file = m/(\w+)/;
   # I then call a subroutine which opens the $data_file
   # and performs some analysis on it
}
[download]

I wasn't surprised the above didn't work, since INP would have to be closed for the other file to be read in the subroutine I called. However, the following did not work also:


open(INP, "<$file_list") or die("Error reading file");
@lines = <INP>;
while (@lines) {
   my $data_file = m/(\w+)/;
   # I then call a subroutine which opens the $data_file
   # and performs some analysis on it
}
[download]

I then get an error on uninitialized values. I could slurp the entire file into a string, and then use split to get the lines, but that seems like it would be costly. Any ideas?

Comment on Multiple files opened Select or Download Code

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Re: Multiple files opened by ahmad (Hermit) on Sep 24, 2010 at 05:28 UTC
Why do you need regex to read lines? `my $data_file = m/(\w+)/;` doesn't make sense to me Here's how you write it : `open(INP, "<$file_list") or die("Error reading file"); while (my $data_file = <INP>) { chomp($data_file); # then call a subroutine which opens the $data_file # and performs some analysis on it }` [download]	[reply] [d/l] [select]
Re^2: Multiple files opened by Anonymous Monk on Sep 24, 2010 at 20:53 UTC
To expand on this: `my $data_file = m/(\w+)/;` assigns a true or false value to the variable indicating whether the regular expression matched. To save the captured value, assign the return value of m// from list context, not scalar context. But if the desired result is to remove the newline, use chomp.	[reply] [d/l]
Re: Multiple files opened by Anonymous Monk on Sep 24, 2010 at 05:59 UTC
INP would have to be closed for the other file to be read in the subroutine Why? The subroutine does not need to use the same file handle name INP, and you can certainly have two files open at the same time. There are limits, but 2 is reasonable. Just make sure you close the file handles - lexical handles will help with that, as it will with file handle name collisions: `open(my $inp, '<', $file_list) or die("Error reading $file_list: $!"); while (<$inp>) { ... } close $inp;` [download] I also don't get why you are using an RE rather than chomp. Anyway, your assignment to `$data_file` probably does not do what you think it does - did you trty printing it out?	[reply] [d/l] [select]
Re^2: Multiple files opened by k_manimuthu (Monk) on Sep 24, 2010 at 07:47 UTC
kokakola613 If you provide the "$file_list" few contents and show your subroutine piece of code, then Monks would be able to give their suggestions efficiently. Please show that.	[reply]
Re: Multiple files opened by changma_ha (Sexton) on Sep 24, 2010 at 08:53 UTC
Hi kokakola613... "I wasn't surprised the above didn't work, since INP would have to be closed for the other file to be read in the subroutine I called. " . I don't think you need to close INP since Perl is intelligent to close it automatically. Also, as ahmad said .you don't need REX to read line...	[reply]