What's happening in this Perl foreach loop? - perl

Question

I have this Perl code:
foreach (#tmp_cycledef)
{
chomp;
my ($cycle_code, $close_day, $first_date) = split(/\|/, $_,3);
$cycle_code =~ s/^\s*(\S*(?:\s+\S+)*)\s*$/$1/;
$close_day =~ s/^\s*(\S*(?:\s+\S+)*)\s*$/$1/;
$first_date =~ s/^\s*(\S*(?:\s+\S+)*)\s*$/$1/;
#print "$cycle_code, $close_day, $first_date\n";
$cycledef{$cycle_code} = [ $close_day, split(/-/,$first_date) ];
}
The value of tmp_cycledef comes from output of an SQL query:
select cycle_code,cycle_close_day,to_char(cycle_first_date,'YYYY-MM-DD')
from cycle_definition d
order by cycle_code;
What exactly is happening inside the for loop?

Answer 1

Huh, I'm surprised no one fixed it for you :)
It looks like the person who wrote this was trying to trim leading and trailing whitespace from each field. It's a really odd way to do that, and for some reason he was overly concerned with interior whitespace in each field despite his anchors.
I think that should be the same as trimming the whitespace around the delimiter in the split:
foreach (#tmp_cycledef)
{
s/^\s+//; s/$//; #leading and trailing whitespace on the whole string
my ($cycle_code, $close_day, $first_date) = split(/\s*\|\s*/, $_, 3);
$cycledef{$cycle_code} = [ $close_day, split(/-/,$first_date) ];
}
The key to thinking about split is considering which parts of the string you want to throw away, not just what separates the fields that you want.

Answer 2

For regex part, s/^\s*(\S*(?:\s+\S+)*)\s*$/$1/ do stripping of leading and trailing whitespaces

Answer 3

Each row in #tmp_cycledef is composed of a string formatted following "cycle_code | close_day | first_date".
my ($cycle_code, $close_day, $first_date) = split(/\|/, $_,3);
Split the string into three parts. The following regular expressions are used to strip leading and trailing whitespaces.
The last instruction of the loop creates an entry in the dictionary $cycledef indexed by $cycle_code. The entry is formated is formatted using the following scheme:
[ $close_day, YYYY, MM, DD ]
where $first_date = "YYYY-MM-DD".

Answer 4

#tmp_cycledef: The output of the sql query is stored in this array
foreach (#tmp_cycledef) : For every element in this array.
chomp : remove the \n char from the end of every element.
my ($cycle_code, $close_day, $first_date) = split(/\|/, $_,3);
split the elements into 3 parts and assign the variable to each of the splited element. parts of split are "split(/PATTERN/,EXPR,LIMIT)"
$cycle_code =~ s/^\s*(\S*(?:\s+\S+)*)\s*$/$1/;
$close_day =~ s/^\s*(\S*(?:\s+\S+)*)\s*$/$1/;
$first_date =~ s/^\s*(\S*(?:\s+\S+)*)\s*$/$1/;
This regex part is sripping of leading and trailing whitespaces from each variable.

Answer 5

my god, it's been such a long time since I've read perl... but I'll give it a shot.
you grab a record from #tmp_cycledef, and chomp off the newline at the end, and split it up into the three variables: then, like S.Mark said, each substitution regex strips off the leading and trailing whitespace for each of the three variable. Finally, the values get pushed into a hash as a list, with some debugging code commented out right above it.
hth

Answer 6

Your query gives a set of rows that
are stored in the array
#tmp_cycledef.
We iterate over each row in the
result using: foreach
(#tmp_cycledef).
The result rows might have trailing
newline char, we get rid of them
using chomp.
Next we split the row (which is not
in $_) on the pipe and assign the
first 3 pieces to $cycle_code,
$close_day and $first_date
respectively.
The split pieces might have leading
and trailing white spaces, the next 3
lines are to remove the leading and
trailing white space in the 3
variables.
Finally we make an entry into the
hash %cycledef. The key use is
$cycle_code and the value is an
array whose first element is
$close_day and rest of the elements
are pieces got after splitting
$first_date on hyphen.