Re: variable mystery

For one thing, your code doesn't run:

Can't use global $_ in "my" at /tmp/tst line 4, near "my $_ "
Execution of /tmp/tst aborted due to compilation errors.
[download]

For another, all you're doing with that "map" statement is returning (via $_) the return of the substitution statement ('1') rather than the modified value of $_ - printing "@fields" would be instructive here.

Lastly, you're explicitly splitting $_ inside your loop; changing the iterator variable is thus going to leave $_ empty, which means that your code isn't going to work. Here's a slightly simpler version of your code, both with an explicit iterator and without:

#!/usr/bin/perl -w
use strict;

for my $foo (<DATA>) {
    my @fields = grep { s/^\s+|\s+$//g; 1; } split /\|/, $foo;
    print "$fields[1]\n";
}

__END__
Baw|Vao|111 Noa St||NewYork|NY|10012|2123456789|123456789
Vca|Wxr|384 Mkl Ln|Xillo|Crrnt Stt|CT|05506|1015567781|1015567782
Uaa|Kvbr|805 Test Rd|Zero|This St|MN|17205|3018757203|3012986736
Caa|Lvbr|905 Test Rd|Bero|That St|MD|12705|3028887203|3028886736
Eaa|Pvbr|311 Zest Rd|Tero|My St|MI|12505|3018757203|3012986736
[download]

#!/usr/bin/perl -w
use strict;

for (<DATA>) {
    my @fields = grep { s/^\s+|\s+$//g; 1; } split /\|/;
    print "$fields[1]\n";
}

__END__
Baw|Vao|111 Noa St||NewYork|NY|10012|2123456789|123456789
Vca|Wxr|384 Mkl Ln|Xillo|Crrnt Stt|CT|05506|1015567781|1015567782
Uaa|Kvbr|805 Test Rd|Zero|This St|MN|17205|3018757203|3012986736
Caa|Lvbr|905 Test Rd|Bero|That St|MD|12705|3028887203|3028886736
Eaa|Pvbr|311 Zest Rd|Tero|My St|MI|12505|3018757203|3012986736
[download]

The output in both cases is:

Vao
Wxr
Kvbr
Lvbr
Pvbr
[download]

Update: I just noticed one more thing: you're using "\r" when you're printing - which means that you're going to overwrite every line that you print. This means that you'll only see the last line, plus anything left over (i.e., anything that was past the current last character) from the previous lines. The correct character to use, at leat in the Unix world, is "\n"; for DOS-based systems, "\n\r" is appropriate.

--
"Language shapes the way we think, and determines what we can think about."
-- B. L. Whorf

Comment on Re: variable mystery Select or Download Code

Replies are listed 'Best First'.
Re^2: variable mystery by ikegami (Patriarch) on Nov 29, 2008 at 02:59 UTC
For one thing, your code doesn't run With 5.10: `>perl -le"for my $_ (1..2) { print }" 1 2` [download]	[reply] [d/l]
Re^2: variable mystery by jeah (Novice) on Nov 29, 2008 at 05:27 UTC
Thanks very much Oko1, sorry I'm not too familiar with perl, I've gone through a book on it and I'm just running through some scenarios to boost my fluency. Every bit of advice helps, like the `"\n\r"` tip. To: Ikegami & Oko1, I'm not sure why you couldn't run the code, I've perl v5.10.0 I can't find the -le 'switch' Ikegami typed, can you tell me a bit about the following line? I really appreciate your advice :) `perl -le"for my $_ (1..2) { print }` [download]	[reply] [d/l] [select]
Re^3: variable mystery by Anonymous Monk on Nov 29, 2008 at 05:37 UTC
C:\>perl -v This is perl, v5.8.7 built for MSWin32-x86-multi-thread ... C:\>perl -MO=Deparse -le"for my $_ (1..2) { print } Can't use global $_ in "my" at -e line 1, near "my $_ " -e had compilation errors. BEGIN { $/ = "\n"; $\ = "\n"; } foreach $_ (1 .. 2) { print $main::_; } C:\strawberry\perl\bin>perl -MO=Deparse -le"for my $_ (1..2) { print } BEGIN { $/ = "\n"; $\ = "\n"; } foreach my $_ (1 .. 2) { print $_; } -e syntax OK C:\strawberry\perl\bin>perl -v This is perl, v5.10.0 built for MSWin32-x86-multi-thread ... [download]	[reply] [d/l]
Re^4: variable mystery by jeah (Novice) on Nov 29, 2008 at 07:21 UTC
Thanks, I guess that's another syntax check I didn't learn. Hi again Oko1, your suggested code has a different syntax, especially the addition of the '1' arg, can you tell me what it does? Thanks. `my @fields = grep { s/^\s+\|\s+$//g; 1; } split /\\|/;` [download]	[reply] [d/l]
Re^5: variable mystery by parv (Vicar) on Nov 29, 2008 at 07:59 UTC
Re^3: variable mystery by ikegami (Patriarch) on Nov 29, 2008 at 12:44 UTC
To: Ikegami & Oko1, I'm not sure why you couldn't run the code heh? I showed it does run in 5.10. `my $_` is a feature introduced in 5.10. I can't find the -le 'switch' Ikegami typed, `-l` sets `$\` to "\n". `-e` causes the following value to be treated as a Perl code to execute. See perlrun	[reply] [d/l] [select]
Re^4: variable mystery by jeah (Novice) on Nov 30, 2008 at 02:29 UTC
Thanks very much for clarifications, everyone. Perl's magical but I need much practice, ugh. :)	[reply]
Re^2: variable mystery by CountZero (Bishop) on Nov 29, 2008 at 08:10 UTC
The correct character to use, at leat in the Unix world, is "\n"; for DOS-based systems, "\n\r" is appropriate. Actually, `\n` works always and Perl will do "The Right Thing" depending on your OS. CountZero A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little or too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity." - The Tao of Programming, 4.1 - Geoffrey James	[reply] [d/l]
Re^3: variable mystery by pobocks (Chaplain) on Nov 29, 2008 at 10:37 UTC
True as long as there's not networking involved... After all, Perl only knows what system it's being served from, not necessarily what system it's serving to. `for(split(" ","tsuJ rehtonA lreP rekcaH")){print reverse . " "}print "\b.\n";`	[reply] [d/l]
Re^2: variable mystery by ikegami (Patriarch) on Nov 29, 2008 at 12:50 UTC
for DOS-based systems, "\n\r" is appropriate. No. `\n` is transformed to `\r\n` on output. `\r\n` is transformed to `\n` on input. So `"\n"` is the appropriate choice for "DOS-based" systems. `>debug file -rcx CX 000A : -d100 la 137B:0100 61 62 63 0D 0A 64 65 66-0D 0A abc..def. +. -q >perl -le"while (<>) { print(unpack('H*', $_)) }" file 6162630a 6465660a` [download]	[reply] [d/l] [select]
Re^2: variable mystery by mandarin (Hermit) on Nov 29, 2008 at 12:52 UTC
The correct character to use, at leat in the Unix world, is "\n"; for DOS-based systems, "\n\r" is appropriate. Shouldn't this be "\r\n", as the DOS line-end is marked by CR LF?	[reply]


laziness, impatience, and hubris
	PerlMonks