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Re: Help to slurp records - $/ maybe?
by Joost (Canon) on May 02, 2003 at 13:38 UTC
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$/='Field 1: ' should work, but it doesn't do what you want: $/ is the end-of-line string, which means that with your data the strings will contain:
Update: first line was wrong:
"Field 1:",
"abc
Field 2: asdfasdf
Field 2: asdfasdfase
Field 2: aaa
Field 3: ss
Field 1: ",
"def
Field 2: abc123
Field 3: blah
Field 1: ",
"asdfa"
You probably want
while(<FILE>) {
next unless /^Field 1/;
# ...
}
To skip everything but Field 1 lines
--
Joost downtime n. The period during which a system
is error-free and immune from user input.
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Well, you're not losing any data (with the $/ trick, that is). The value of the $/ variable is also put at the end of the read 'line'.
If you want to lose that data, use chomp(), it will remove your current line-terminator.
The only actual problem is matching the first line.
--
Joost downtime n. The period during which a system
is error-free and immune from user input.
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Re: Help to slurp records - $/ maybe?
by Aristotle (Chancellor) on May 02, 2003 at 14:38 UTC
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I'd stick with the conventional approach here. All else is bound to be a dirty/bad hack. You don't like redo? Fine, you can use a nested loop.
local $_;
do {
my $rec = '';
do {
$rec .= $_ = <>;
} until /^Field 3/ or !defined;
# ...
} while defined;
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Re: Help to slurp records - $/ maybe?
by JaWi (Hermit) on May 02, 2003 at 13:52 UTC
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You could use the following (coarse, not fully tested, yada yada yada) approach:
#!/usr/bin/perl -w
use strict;
use warnings;
my $data;
{
local $/ = undef;
$data = <DATA>;
}
print "Record: [$1]\n"
while ( $data =~ /(Field 1:.*?Field 3:[^\n]+)/sg );
__DATA__
Field 1: abc
Field 2: asdasdasdf
Field 2: asdsaads
Field 2: asdf
Field 3: asfssadfsad
Field 1: abc
Field 2: asdf
Field 3: asfssadfsad
Field 1: abc
Which outputs:
Record: [Field 1: abc
Field 2: asdasdasdf
Field 2: asdsaads
Field 2: asdf
Field 3: asfssadfsad]
Record: [Field 1: abc
Field 2: asdf
Field 3: asfssadfsad]
Record: [Field 1: abc
Field 2: asdasdasdf2
Field 2: asdf3
Field 3: asfssadfsad]
HTH,
-- JaWi
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JaWi,
Thanks - I already know that trick. The problem is it isn't
scalable. The larger the file is that you are slurping the
more memory you need to have. I am processing logs that are
in the vincinity of a gigabyte and have millions of records.
Cheers - L~R
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Re: Help to slurp records - $/ maybe?
by hmerrill (Friar) on May 02, 2003 at 13:38 UTC
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IMHO, simpler is better - stick with the iterative approach as it will be much easier for you and anyone else who looks at the code to understand and maintain it 6 months or a year from now when it needs to be changed.
What you don't want to do is create some obfuscated code that takes someone a day to understand an another day to fix. Make it as simple as possible for *any* Perl person to understand.
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hmerrill,
IMHO, it is much simpler to have $/ = ""; than it
is to have labels, redo statements, and variable flags.
Cheers - L~R
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If $/ = ""; works, great. But it won't for the problem as you stated.
What happens when someone needs to insert a 'Field 2b' in the format six months down the road? You would have to fully rewrite a grok-at-once gimmick, but you'd only have to add the support for a new field type if it were a sensible loop.
--
[ e d @ h a l l e y . c c ]
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Debatable - I do conceed that the iterative approach means more code, keeping track of flags, etc. - it's not pretty. But I'd have to see a finished slurp example setting $/ = "" before judging that to be the better option. In all likelihood the slurp example may indeed come out on top, but its ease of understanding and maintainability would be greatly enhanced by a generous comment spelling out exactly what the thing does. Whatever you decide on as the final winner, post in this thread.
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Re: Help to slurp records - $/ maybe? (or flip-flop)
by broquaint (Abbot) on May 02, 2003 at 15:25 UTC
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Sounds like a great use of the flip-flop operator
my($i, @data) = 0;
until(eof FILE) {
$data[$i] .= $_
while ($_ = <FILE>) and /^Field 1/ .. /^Field 3/;
$i++;
}
See. perlop for more info.
HTH
_________
broquaint | [reply]
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Re: Help to slurp records - $/ maybe?
by jgallagher (Pilgrim) on May 02, 2003 at 14:55 UTC
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This is quite ugly, but I have to go to work and this is just the first thing that popped into my head. It uses the local $/ like you described.
#!/usr/bin/perl -w
use strict;
local $/ = "\nField 1: ";
my $data = <DATA>;
$data =~ s/Field 1: $//;
chop($data);
print "[$data]\n";
while (<DATA>) {
s/Field 1: $//;
$_ = "Field 1: $_";
chop;
print "[$_]\n";
}
__DATA__
Field 1: abc
Field 2: asdfasdf
Field 2: asdfasdfase
Field 2: aaa
Field 3: ss
Field 1: def
Field 2: abc123
Field 3: blah
Field 1: asdfa
Output is:
[Field 1: abc
Field 2: asdfasdf
Field 2: asdfasdfase
Field 2: aaa
Field 3: ss]
[Field 1: def
Field 2: abc123
Field 3: blah]
[Field 1: asdf]
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