Paul, thank you very much for your helpful reply. To answer your question, I am
certain that the first two matches worked because I produced the output I
showed with:
[EMAIL PROTECTED] UScensus]$ perl -ne 'print if
/^.{8}150.{18}24510.{21}(.{6})(.)/;' mdgeo.uf1 |head -1
uSF1 MD15000000 009214935522451020 9 0101001
88722397N07209999900
116759 0Block Group 1
S 1158
662+39283007-076574503
[EMAIL PROTECTED] UScensus]$
Sorry if I left out this information and wasted anyone's time.
A person responded to me privately and suggested this modification, which seems
to work fine:
[EMAIL PROTECTED] UScensus]$ perl -ne 'print "Tract $1 BLKGRP $2\n" if
/^.{8}150.{18}24510.{21}(.{6})(.)/;' mdgeo.uf1 |head -3
Tract 010100 BLKGRP 1
Tract 010100 BLKGRP 2
Tract 010100 BLKGRP 3
[EMAIL PROTECTED] UScensus]$
I've been bitten by this bug before and can never remember the solution to when
variables are assigned values. I thought assigning them in a previous command
would have worked, but I must have overlooked something.
Thank you, again, for your help.
-Kevin
-----Original Message-----
From: Paul Lalli [mailto:[EMAIL PROTECTED]
Sent: Tuesday, February 26, 2008 3:41 PM
To: beginners@perl.org
Subject: Re: Why doesn't this work: matching capturing
On Feb 26, 1:19 pm, [EMAIL PROTECTED] (Kevin Zembower) wrote:
> I have a data file that looks like this:
> uSF1 MD15000000 009214935522451020 9 0101001
> 88722397N07209999900
> 116759 0Block Group 1
> S 1158 662+39283007-076574503
>
> uSF1 MD15000000 009215035522451020 9 0101002
> 88722397N07209999900
> 109338 0Block Group 2
> S 842 547+39280857-076573636
>
> uSF1 MD15000000 009215135522451020 9 0101003
> 88722397N07209999900
> 182248 135142Block Group 3
> S 920 442+39279557-076574311
>
> This is actually three lines that all start with 'uSF1'. This is the
> Summary File from the US 2000 Census. I want to print all the census
> tracts and blockgroup numbers for FIPS state code = "24" (Maryland) and
> FIPS county code "510" (Baltimore City) for summary level '150'. These
> are all fixed-length records. I tried:
> [EMAIL PROTECTED] UScensus]$ perl -ne '($tract, $bg) =
> /^.{8}150.{18}24510.{21}(.{6})(.)/; print "Tract $tract BLKGRP $bg\n";'
> mdgeo.uf1 |head
> Tract BLKGRP
> Tract BLKGRP
> Tract BLKGRP
> <snip>
>
> I thought that this would:
> skip 8 characters and match '150'
> skip 19 more characters and match '24' and '510'
> skip 21 more characters and capture the next 6 in $tract
> capture the next character in $bg
> and print them.
>
> The first two matches work, but nothing is captured. Any ideas what I'm
> doing wrong?
On what do you base your assumption that "the first two matches
work"? Nothing in your code or output indicates that, as you are
never checking the return value of the pattern match.
FWIW, your code did work for me when I copy and pasted your sample
text, and joined the lines as they should have been. Therefore, I
think it's pretty likely that your datafile does not contain what you
think it does. I think it's more likely that the one line you think
you have that starts with uSF is actually broken up into a few lines.
Try some debugging prints of $_ to see what you actually have, like:
print "Line $.: <<$_>>";
Try checking the return value of your regexp:
/^.{8}150.{18}24510.{21}(.{6})(.)/ and print "Tract $1 BLKGRP $2\n";
Try enabling warnings to see of your two variables are undefined
(which they would be if the pattern didn't match) or just empty
strings (which they would be if the pattern matched but nothing was
captured - this, of course, isn't possible, since a six-character
match can't possibly be the empty string).
Paul Lalli
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