a)
> open (BHF_FILE, "</home/bob/tmp/md5music")
The modern way to open a file is to:
1) Use the three argument form of open().
2) Create a variable for the file handle.
open (my $BHF_FILE, '<', '/home/bob/tmp/md4music');
while (my $line = <$BHF_FILE>) {
#do something with $line
}
close $BHF_FILE;
b) Take a look at this code:
use strict;
use warnings;
use 5.010;
my $line = 'hello world goodbye';
my @pieces = split / /, $line, 2;
for (@pieces) {
say;
}
--output:--
hello
world goodbye
At the command line, you can always type:
perldoc -f <a function name>
to get more information about a function. For instance:
$ perldoc -f split
c) To access the first element of an array, you do this:
my @data = ('hello', 'world', 'goodbye');
say $data[0];
Compare the second line to the expression: $1[$i]. Just like $data[0]
is accessing an element of the array @data, the expression $1[$i] is
trying to access an element of the array @1. And unless you defined
an array called @1 in your code, that will cause an error.
perl does automatically define variables called $1, $2, etc., which
are assigned portions of a regex match, however they are not arrays.
The $ sign in front of the names 1, 2, etc. tells you that they are
variables that store scalar values (= a single value).
On 1/30/10, Rob Dixon <rob.di...@gmx.com> wrote:
> Hi Bob
>
> I suggest you forget about regular expressions and use the library
> function split() instead. Take a look at the code below.
>
> HTH,
>
> Rob
>
>
>
> use warnings;
> use strict;
>
> my (@ukchecksum, @uktrackname);
>
> open my $bhf_file, '<', '/home/bob/tmp/md5music'
> or die "Could not open md5music: $!";
>
> while (<$bhf_file>) {
>
> my @fields = split ' ', $_, 2;
>
> if (@fields < 2) {
> print "Invalid data format at line $.\n";
> next;
> }
>
> push @ukchecksum, $fields[0];
> push @uktrackname, $fields[1];
> }
>
> print $ukchecksum[0];
> print $uktrackname[0];
>
>
>
> Bob Williams wrote:
>> Hi,
>>
>> I am trying to split the lines in a file into two halves (at the first
>> space) each half going into an array. The code I have written is below.
>> The
>> print command is there to test that things worked correctly, but it only
>> gives an error for each instance of the print command...
>>
>> Use of uninitialized value within @uktrackname in print at
>> /home/bob/Documents/scripts/perl/music_md5_compare.pl line 22 (#1)
>>
>> ---Code---
>> #!/usr/bin/perl
>> use warnings;
>> #use strict;
>> #use diagnostics;
>>
>> # perl script to compare two files of md5 checksums
>> #+and extract the lines which differ
>>
>> open (BHF_FILE, "</home/bob/tmp/md5music")
>> or die "Could not open md5music: $!";
>> @bhffile = <BHF_FILE>;
>> close (BHF_FILE);
>>
>> for (my $i = 0; $i <= $#bhffile; $i++){
>> $bhffile[$i] =~ m/(\s.+) ( .+)/;
>> push @ukchecksum, $1[$i];
>> push @uktrackname, $2[$i];
>> }
>>
>>
>> print @ukchecksum[0]; # Won't print - uninitialized value ???
>> print @uktrackname[0]; # Won't print - uninitialized value !!!
>> ---Code---
>>
>> What am I doing wrong?
>>
>> Many thanks,
>>
>> Bob
>
>
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