If you're on a Unix/Linux/Mac, type perldoc perl into a terminal window, and see all the documentation you already have installed on your machine. ( I dunno how to view it on MSDos, but I'd try typing the same thing in a cmd shell. ) or you can go to CPAN or ask google to find 'perl pod'. perlsyn is the section which actually discusses syntax.

Briefly, there is almost never a reason to use the C style for loop. If you want to iterate over a list, let Perl handle the hard part:

for my $elem ( @$mysql ) {
    my $field1 = $elem->{field};
}
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If you want to keep track of the index number, use the range operator, let Perl handle the hard part:

for my $idx ( 0..@$mysql ) {
    my $field1 = $mysql->[$idx]{field1};
}
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Notes: If you specify an array in a scalar context, Perl decides you want to know how many elements there are in the array. The range operator is definitely a scalar context, it expects a number on the left and a number on the right. I frequently use scalar @array, so others will decipher what I'm doing more easily; some people think the superfluous 'scalar' is bad ( Hi Mike ).

Some people differentiate between 'for' and 'foreach'; they must love typing. I use 'for' for both, since Perl considers them synonyms.

You don't need to quote hash tags, you can use the bare text; similarly, the bare characters before a fat arrow are automatically taken as a string:

use 5.010;
$tag = 'Homer';
my %h = ( $tag => 'woohoo!', Fred => 'YABA DABA DOO!' );
say  Dumper(\%h);

# outputs:
# $VAR1 = {
#          'Homer' => 'woohoo!',
#          'Fred' => 'YABA DABA DOO!'
#        };
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for my $idx ( 0..@$mysql ) {
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Of course, that should read:

for my $idx ( 0..@$mysql-1 ) {
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No, it should read:

for my $idx ( 0..$#$mysql ) {
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Thank you.

As Occam said: Entia non sunt multiplicanda praeter necessitatem.

I use a mix of both. If I need to know the actual index in the loop for something I'm doing, the first works. If I'm just iterating over the elements and don't necessarily need to know the index, I use the second.

Perl 5.12 added the capability for each to return the index and value of an array in list context.

If you need to know the index and are using an increment of 1 then:

for my $index (0 .. $#$mysql) {
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is much better than the C for loop variant. About the only time a C loop is likely to be used in Perl is when the "increment" is not 1 or the termination condition is not simply reaching an end point, although there are often better ways of achieving both objectives than using a C for loop.

Update: $#$mysql per eyepopslikeamosquito's catch

True laziness is hard work

for my $index (0 .. $#mysql) {
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Of course, that should read:

for my $index ( 0..$#$mysql ) {
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If you work with DBI, using a while-loop may be more efficient than reading the entire result set into memory and iterating over it using a for loop. See $sth->bind_columns() and the last paragraph in $sth->fetchall_arrayref(): A standard while loop with column binding is often faster because the cost of allocating memory for the batch of rows is greater than the saving by reducing method calls. It's possible that the DBI may provide a way to reuse the memory of a previous batch in future, which would then shift the balance back towards fetchall_arrayref().

Try Devel::NYTProf to find out if that difference is really relevant for your application. Note that NYTProf will very likely show you the real bottlenecks in your application.

Alexander