Parsing Test File

gri6507 has asked for the wisdom of the Perl Monks concerning the following question:

I have a text file that has a structure like this:

A=[1,
2,
3,
4
]
[download]

I am trying to parse the file until that last "]". I know a long way of doing this, but I want to know why this doesn't work

open(FIL, $file) || die "can't open file $^E\n";
while(chomp($_ = <FIL>) ne "]"){
  #do stuff
}
[download]

Apparently, the While loop is never terminated, and reads past the end of the file. Any ideas?

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Re: Parsing Test File by VSarkiss (Monsignor) on Jan 15, 2002 at 21:05 UTC
You're not testing for end-of-file, which is indicated by an `undef` return from the diamond operator. Breaking up your logic to test for EOF will guarantee that it'll stop, even if the file doesn't contain the string you expect. Plus it'll be easier to understand: `while (<FIL>) { chomp; last if $_ eq ']'; # It's also possible to do "last if /^\]$/", but # all you need is a simple string compare. # do stuff }` [download] HTH	[reply] [d/l] [select]
Re: Parsing Test File by davis (Vicar) on Jan 15, 2002 at 20:57 UTC
Chomp returns the number of characters removed, not the actual characters removed. Chomp will also only remove the $/ , or input record seperator variable. Replacing the chomp with chop might do as you expect. See perlvar and perlfunc for more information Hope this helps davis Update The reply by Vsarkiss makes more sense.	[reply]
Re^2: Parsing Test File by Aristotle (Chancellor) on Jan 15, 2002 at 23:00 UTC
Just for completeness' sake, I'd like to mention one should always prefer chomp over chop for stripping end-of-line characters. The most obvious example of why is if the last line in the file has no trailing newline. In that case chop will break - it will eat a character from your payload. chomp will still do the right thing (which is nothing, in this case). Unless you really want to remove the last character of every line, regardless of what that may be, you shouldn't chop.	[reply]
Re: Re: Parsing Test File by gri6507 (Deacon) on Jan 15, 2002 at 21:05 UTC
thank you. That makes perfect sense.	[reply]
Re: Parsing Test File by broquaint (Abbot) on Jan 15, 2002 at 21:07 UTC
There are several more suitable solutions for parsing the provided example `my($data) = $input =~ /\[([^\]]+)\]/s;` [download] or if you want to be really thorough you could try the `Text::Balanced` module by Damian Conway. Also you probably want to use `$!` instead of `$^E` as it's more portable and pretty much the excepted standard. HTH broquaint	[reply] [d/l]
Re: Parsing Test File by talexb (Chancellor) on Jan 15, 2002 at 21:25 UTC
In addition to the various ways already mentioned, you could also `undef $/;` and then (Camel, 3rd edition, p.666) read the file into a single scalar, replacing new lines with spaces. Then you could parse on strings bounded by pairs of `[]`. TMTOWTDI. :) --t. alex "Of course, you realize that this means war." -- Bugs Bunny.	[reply] [d/l] [select]