Hi John,
a few comments on your code (some of which was derived from the OP's).
On Mon, 01 Aug 2011 00:26:29 -0700
"John W. Krahn" <jwkr...@shaw.ca> wrote:
> homedw wrote:
> > hi all,
>
> Hello,
>
>
> > i want to open some files in a directory, you can see the details below,
> >
> > #!/usr/bin/perl -w
> > use strict;
> > opendir (FH,'C:\Player');
> > chdir 'C:\Player';
> > for my $file(readdir FH)
> > {
> > open DH,"$file";
> > foreach my $line(<DH>)
> > {
> > while($line=~/"a=(\d),b=(\w+)"/gi)
> > {
> > $sum+=$2-$1;
> > }
> > }
> > }
> > print "$sum\n";
> >
> >
> > I can't open the files in 'C:\Player', can you help me find out where the
> > problem is?
>
> Use error checking on your system calls and let the system tell you what
> the problem is:
>
>
> #!/usr/bin/perl
> use warnings;
> use strict;
>
> opendir FH, 'C:\Player' or die "Cannot opendir 'C:\\Player' because: $!";
> chdir 'C:\Player' or die "Cannot chdir to 'C:\\Player' because: $!";
>
1. You have used the string 'C:\Player' several times. Better put it in a
variable:
my $dir_name = 'C:\Player';
Then you can use it or interpolate it.
2. You can also use '/' on Windows instead of '\' which gives fewer problems
when interpolating into qq{..} and other strings like that.
3. "FH" is generally short for "file-handle", but here it is a directory handle.
4. It should be a lexical variable:
opendir my $dir_handle, $dir_name
or die "Cannot open '$dir_name' because: $!";
> for my $file ( readdir FH )
This will slurp the entire directory contents into one big list and iterate
over it. A somewhat less memory consuming version is:
while (my $file = readdir($dir_handle))
which would read it in scalar context.
Also see: File::Spec->no_upwards: http://perldoc.perl.org/File/Spec.html .
> {
> open DH, '<' $file or die "Cannot open '$file' because: $!";
1. "DH" is short for "directory handle" and in this case it's a file handle.
2. It isn't lexical.
3. You're missing a comma between the «'<'» and the «$file».
4. This program will always throw an exception because it will try to open the
directory entries "." and/or ".." for reading, which will fail because they are
not files.
> foreach my $line ( <DH> )
This will slurp the entire file into memory as a list/array of lines and then
iterate over it. Better write it as:
while (my $line = <$file_handle)
> {
> while ( $line =~ /"a=(\d),b=(\w+)"/gi )
> {
> $sum += $2 - $1;
> }
$sum was not declared anywhere and the regular expression is a bit strange for
what one dos with $1 and $2 later.
Regards,
Shlomi Fish
> }
> }
> print "$sum\n";
>
> __END__
>
>
>
> John
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