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Re: I need help with opening a directory and reading files in that directory.

by shadowsong (Monk)
on Sep 04, 2015 at 23:18 UTC ( #1141070=note: print w/replies, xml ) Need Help??


in reply to I need help with opening a directory and reading files in that directory.

Brandon,

Welcome to the Monastery. Let's see if we can get your script working as expected - let us break it down one step at a time and solve each problem in turn.

I'm having a hard time creating/reading the files to do something with and create the $hash{$key} = $values. But, is there a way to use <> to open the directory path

We do not use <> when opening a directory path. Here is a small script to open a directory, read the contents of that directory and list/print the files therein

#! perl -slw use strict; opendir DH, "." or die $!; # open current directory while($_ = readdir(DH)){ # don't evaluate special dirs '.' & '..' next if $_ eq "." or $_ eq ".."; print "$_"; # print this file/directory's name } __END__

One can also use a construct known as a glob to evaluate the contents of a directory

#! perl -slw use strict; my @files = glob("*"); print "Files matched via glob pattern *: @files\n"; __END__
and then use the <> to read the files and do something with the information.

Reading files and doing something with the information is relatively straightforward (but beware this can get hairy real fast based on what your particular environment is like - let's keep it simple for now. It's enough that you've been made aware that what we're doing here is scratching the surface).

#! perl -slw use strict; opendir DH, "." or die $!; # open current directory while($_ = readdir(DH)){ # don't evaluate special dirs '.' & '..' next if $_ eq "." or $_ eq ".."; print "$_"; # print this file/directory's name # as a by-product of readdir; use the file's stat info # to check whether this is indeed a regular file we can # open for reading/further processing if (-f $_) { open FH, "<$_" or die $!; print "output for file: $_\n"; while (my $line = <FH>) { print $line; } close FH; } } __END__

Let us know if you have any issues w/ the syntax for using a hash.

p.s. Careful when using RegExps; certain characters carry special meaning and need to be "escaped". So instead of having

if ($filename =~ /.txt/)

You might want to have:

if ($filename =~ /\.txt/)

Replies are listed 'Best First'.
Re^2: I need help with opening a directory and reading files in that directory.
by brawal128 (Novice) on Sep 05, 2015 at 01:15 UTC

    Thanks shadowsong. I was looking through the perldocs and did see a lot of the information that you presented. It does help to get others opinion on this because the instructor that I have was telling me to us @ARGV to open the directory. That confused me even more because I had just did another assignment that parsed two files and did something with those files. But, the files were local to the .pl file I wrote. So, you could get away with that.

    I figured that the glob or opendir would work just you look stated and based on the research I did on the internet and this site. So, I'm assuming that you can replace the $_ default variables with any name that you want. I do like how you explained the information on using stat info to see if it really is a file that we want to look at. I will get to work on fixing what I have created and I will let you guys know how it goes.

    Thanks, Brandon

      So, I'm assuming that you can replace the $_ default variables with any name that you want.

      Yes. But let's be clear. The name of the variable is kind of irrelevant here. The contents of the variable hold the name of the file being processed, which is probably more interesting to you.

      Most solutions, including the one presented to you, will loop through a list of data (like names of files) and then assign the different data to the same variable each time through the loop. Perl provides the default variable $_, but you can declare a variable of your own with your own name if you wish (I'm not sure this is what you meant, but maybe it was).

      A good rule of thumb is that if you need to write out $_, to be clear, you should assign a variable name. Usually you don't need to write it out as it is implicitly handed to functions, e.g. as in:

      while (<$FH>) { print; # prints the current line using $_ implicitly }
      But if you need to or want to use a variable name of your choice, you can. (Also recommended is the 3-argument form of open):
      while ( my $filename = readdir(DH) ) { next if $filename eq '.' or $filename eq '..'; print $filename; if ( -f $filename ) { open my $FH, '<', $filename or die "open: $!\n"; while ( my $line = <$FH> ) { print $line; } close FH or die "close: $!\n"; } }
      But the "any name you want" applies to the variable ... if you are looking for a particular name, as in a piece of data, you'll have to loop through and find it. While you can certainly say:
      if ( -f 'The Bravery-Believe.txt' ) { # do something }
      . . . it wouldn't make sense to do that in a loop through a list, as you'd be asking each element of the list about a certain other element, when they don't "know anything about each other."

      What you might do is check to see if you are dealing with the file you want and skip the rest: then you would have use for the specific filename, which is what I think you might be getting at:

      my $wanted = 'The Bravery-Believe.txt'; while ( my $filename = readdir(DH) ) { next unless $filename eq $wanted; # do something . . . }
      Hope this helps build on shadowsong's answer.

      The way forward always starts with a minimal test.
Re^2: I need help with opening a directory and reading files in that directory.
by brawal128 (Novice) on Sep 08, 2015 at 15:22 UTC

    Shadowsong, this is what I came up with. The directory is being read and information is being stored in memory, but I'm have having trouble opening the .txt files to read the data in those files. I thought I was doing it the right way by using hashes to keying a value. But, it is still not reading the data in the .txt file. Am I doing something wrong or am I still not reading what is in the file?

    #!/usr/bin/perl -slw use strict; use warnings; use Data::Dumper; my %length; my %songs; opendir DH, "Y://perlscripts2/software/perl2/music" or die $!; # open +current directory while($_ = readdir(DH)){ # don't evaluate special dirs '.' & '..' next if $_ eq "." or $_ eq ".."; if ($_ =~ /\.txt/){ chomp $_; my ($artist, $song_title) = split '-', $_, 3; $length{$artist}{$artist} = $artist; $length{$artist}{$song_title} = $song_title; print "$_"; # print this file/directory's name } # as a by-product of readdir; use the file's stat info # to check whether this is indeed a regular file we can # open for reading/further processing if (-f $_) { open FH, "<$_" or die $!; print "output for file: $_\n"; while (my $line = <FH>) { print "$line\n"; if ($line =~ /\.txt/){ my($album, $minutes, $seconds, $genre) = split ':', $l +ine, 4; $songs{$album} = $album; $songs{$minutes} = $minutes; $songs{$seconds} = $seconds; $songs{$genre} = $genre; print $album, "\n"; } close FH; } } }closedir DH; foreach my $artist ( sort keys %length ) { print "$artist is the name of the Artist\n"; } foreach my $album ( sort keys %songs ) { print "$album is this now\n"; }

    Thanks, Brandon

      Brandon,

      Let's looks at the solution you have come up with; but before we do - just a quick note:

      #!/usr/bin/perl -slw use strict; use warnings;

      The use warnings; pragma is redundant if you supply the -w switch
      --

      Now, looking at your solution we can see that you've opened a target directory and proceeded to read its contents via the excerpt below:

      opendir DH, "Y://perlscripts2/software/perl2/music" or die $!; # open +current directory while($_ = readdir(DH)){ # don't evaluate special dirs '.' & '..' next if $_ eq "." or $_ eq "..";

      What comes next is a bit peculiar..

      if ($_ =~ /\.txt/){ chomp $_; my ($artist, $song_title) = split '-', $_, 3; $length{$artist}{$artist} = $artist; $length{$artist}{$song_title} = $song_title; print "$_"; # print this file/directory's name }

      What you're saying above is to match filenames with ".txt" in them. Are you sure this is what you want to do? Do you have ".txt" embedded within your music filenames?

      Notwithstanding your expectations of the existence of a ".txt" filename which you'd like to process in your music files directory - you should be doing that check within the 2nd if (-f $_) conditional; so you only check legitimate regular files for the ".txt" string.

      Here's a small script I wrote to process some flac files within one of my music directories (which is devoid of any ".txt" files)

      #! perl -slw use strict; use Data::Dumper; $Data::Dumper::Sortkeys = 1; my ($id,$songs_ref,$artists_ref,$albums_ref,%songs,%artists,%albums); opendir DH, "D:/music/Alice In Chains/2001 - Greatest Hits" or die $!; # open current directory while($_ = readdir(DH)){ # don't evaluate special dirs '.' & '..' next if $_ eq "." or $_ eq ".."; # music files in this directory are *.flac files with the # naming style: <track#> - <band> - <album> - <track.flac> # no need to check stat info - we're processing files that # end in .flac (notice the end-of-line match char '$'?) if (m{\.flac$}){ # tip: m{..} is another way of saying /../ # add .flac to the split pattern so that it is not # included in our "<track>" field my ($track_num, $band, $album, $track) = split / \- |\.flac/; # increment our hash ref id so we don't overwrite entries $id++; # ------------------------------------------------------- # Example Using Hash References # ------------------------------------------------------- $songs_ref->{$id}->{TITLE} = $track; $songs_ref->{$id}->{ARTIST} = $band; $songs_ref->{$id}->{FAVOURITE} = 1 if $track eq 'Would'; $songs_ref->{$id}->{TRACK_LENGTH} = undef; # to do later $artists_ref->{$id}->{NAME} = $band; $artists_ref->{$id}->{SONGS}->{TITLE} = $track; $artists_ref->{$id}->{SONGS}->{ALBUM} = $album; $albums_ref->{$id}->{ARTIST} = $band; $albums_ref->{$id}->{NAME} = $album; $albums_ref->{$id}->{SONGS}->{TITLE} = $track; $albums_ref->{$id}->{SONGS}->{TRACK_NUM} = $track_num; # ------------------------------------------------------- # Example Using Hashes # ------------------------------------------------------- $songs{$id}{TITLE} = $track; $songs{$id}{ARTIST} = $band; $songs{$id}{TRACK_LENGTH} = undef; # to do later $artists{$id}{NAME} = $band; $artists{$id}{SONGS}{TITLE} = $track; $artists{$id}{SONGS}{ALBUM} = $album; $albums{$id}{ARTIST} = $band; $albums{$id}{NAME} = $album; $albums{$id}{SONGS}{TITLE} = $track; $albums{$id}{SONGS}{TRACK_NUM} = $track_num; } } closedir DH; # use perl's object data serializer to view our data print Dumper $songs_ref; print Dumper $artists_ref; print Dumper $albums_ref; print Dumper \%songs; print Dumper \%artists; print Dumper \%albums; __END__

      I would like to focus on why it is you're not getting those ".txt" files open for processing, but to do that we need to establish which files are in the directory that you're reading from? Have a look at the example provided and if you find it's still necessary to open and read some kind of ".txt" file - please provide us with the output of dir "Y://perlscripts2/software/perl2/music"

      Good luck!

        Shadowsong, here is the output of my directory. I know that music files don't consist of .txt extensions, but this is what I was asked to do for the assignment. So, I made these files names up and went with this type. Inside the files there is supposed to one line that contains the album, minutes, seconds, and genre each separate by ":". The Sun and the Moon:3:47:Alternative

        OUTPUT of DIRECTORY:<\p>

        The Bravery-Believe.txt

        output for file: The Bravery-Believe.txt

        The Bouncing Souls-True Believers.txt

        output for file: The Bouncing Souls-True Believers.txt

        The Kickdrums-Atonement.txt

        output for file: The Kickdrums-Atonement.txt

        I'm assuming that this:

        if ($_ =~ /\.txt/){ chomp $_; my ($artist, $song_title) = split '-', $_, 3; $length{$artist}{$artist} = $artist; $length{$artist}{$song_title} = $song_title; print "$_"; # print this file/directory's name

        Could be part of this:

        open FH, "<$_" or die $!; print "output for file: $_\n"; while (my $line = <FH>) { print $line; chomp $line; if ($line =~ /\.txt/){ my $artist; my ($album, $minutes, $seconds, $genre) = split ':', $line, 4; $length{$artist}{album} = $album; $length{$artist}{minutes} = $minutes; $length{$artist}{seconds} = $seconds; $length{$artist}{genre} = $genre; print $album, "\n"; }

        So, I'm still trying to open the FH of the .txt file and read the contents to get the total amount of the song length for each line and print it out. "Saying this Artist has a total amount of Music". I really appreciate your guidance and patience with me. I know I am a newby at this, but I'm willing to put the time in to learn and get the most out of this language. Thanks, Brandon

      opendir DH, "Y://perlscripts2/software/perl2/music" or die $!; while($_ = readdir(DH)){ ... if (-f $_) {

      The file test will work when the value being tested is a path which can be accessed from the current directory where the program was started. As is, $_ contains only the bare file name, devoid of directory name.

      open FH, "<$_" or die $!; print "output for file: $_\n"; while (my $line = <FH>) { ... if ($line =~ /\.txt/){ ... } close FH; }

      A closure of the file handle while still iterating over it will result in "readline() on closed filehandle" (perl 5.16.2) error message, causing premature demise of the program. If the file handle needs to be closed early, then should skip the whole loop via last.

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