my $line = ";field;;field;\t;field; ;field;field";
my @line = split ";", $line;
my @null = grep { defined $_ } map { $line[$_] =~ /^$/ ? $_ : undef } 
+(0..$#line);

print "line contains ", scalar @null, " null fields at offset(s): @nul
+l";
#line contains 2 null fields at offset(s): 0 2
[download]

use strict;

while ( <DATA> )
{
    my @line = split /\|/, $_;
    my @null = grep { defined $_ } map { $line[$_] =~ /^$/ ? $_ : unde
+f } (0..$#line);
    print "line contains ", scalar @null, " null fields at offset(s): 
+@null\n";
}

#line contains 3 null fields at offset(s): 1 3 4
#line contains 2 null fields at offset(s): 2 4
#line contains 3 null fields at offset(s): 0 1 4
#line contains 2 null fields at offset(s): 1 2 4

__DATA__
first||third||
alpha|beta||delta|
||c|d|
one|||four|
[download]

holli++

Here's a humble for loop:

#!/usr/bin/perl

use strict;
use warnings;

my $line = "a||c|\t|  |d||e";
my @fields = split(/\|/, $line);
my @null;

for my $i (0..$#fields){
  push @null, $i unless $fields[$i];
}

print "null fields: ", scalar @null, "\n";
print "at field: ";
print ++$_, ", " for @null;

# output
# null fields: 2
# at field: 2, 7,
[download]

holli and wfsp, great answers. Now, I'd like to make this snippet of code more general by turning the delimiter into a variable. But doing so doesn't work (I'm struggling to understand regular expressions).

my $delim = '|';
my $line = "a||c|\t|  |d||e";
my @fields = split(/\\$delim/, $line);

# output
# null fields: 0
# at field:
[download]

I posted as anon by mistake, which means I can't edit my post to remove the superfluous line containing the variable "line".

I ended up doing this in awk; it could probably be translated to perl by someone smarter than me. For some reason the filename is printed AFTER the results instead of before as I would have expected, but otherwise this seems to work.


BEGIN{FS="\|";}
{
   line= substr($0,0,length($0)-1); #peel trailing bar
   n=split($0,a);
   for (i=0;i<n;i++){
      line=line  a[i];
      if(a[i] ==""){nulls[i]++};
   }
}
END{
   print FILENAME;
   for (i in nulls) print "\t field " i": " nulls[i] " nulls";
}
[download]

They look like this:

first||third||
alpha|beta||delta|
||c|d|
one|||four|

I'd like to print something like:
field1->1
field2->2
field3->2
field4->1

Build a hash

#!/usr/bin/perl

use strict;
use warnings;

my %null;

while (<DATA>){
  my @fields = split(/\|/);
  for my $i (0..$#fields){
    $null{"field$i"}++ unless $fields[$i];
  }
}

for my $key (sort keys %null){
  print "$key->$null{$key}\n";
}

__DATA__
first||third||
alpha|beta||delta|
||c|d|
one|||four|
[download]

output:

field0->1
field1->3
field2->2
field3->1
[download]

The field numbers start at zero but also the second field has 3 compared to 2 in your desired ouput.

The third line of your data starts with two bars, isn't that 2 null fields?

How does "first||third||" fit together with "field1->1"? There are 3 null fields in that line.


holli, /regexed monk/

Update: Misinterpretated the OP last comments.

I think you should consider looking for tabs and whitesapce on each line too.

Maybe I'm wrong, but if you could provide some sample data, then I'm sure we can help.