Unknown warnings/errors

kmullin5016 has asked for the wisdom of the Perl Monks concerning the following question:

I am a perl newbie, but I inherited a very large perl program, and am learning a lot from it. I added the line:

use strict;

to take advantage of the additional warnings and errors I get from it. But, now at run time, I am seeing this message (among others)

Use of uninitialized value in pattern match (m//) at secalert_index_verbose.cgi line 180.

Now this is the code before and after line 180:

($ENV{HTTP_USER_AGENT} =~ /MSIE/)
&& do {
  # Internet Explorer
  $style{'body','font-size'}='10pt';
  $style{'th','font-size'}='8pt';
  $style{'td','font-size'}='6pt';
  $style{'pre','font-size'}='10pt';
  $titlebox_size='4';
  1;
} || do {
  # Netscape
  $style{'body','font-size'}='10pt';
  $style{'th','font-size'}='10pt';
  $style{'td','font-size'}='8pt';
  $style{'pre','font-size'}='10pt';
  $titlebox_size='5';
};

Line 180 is actually the line that reads:

} || do {

What's it talking about, and how do I fix it? I can't find the string 'm//' anywhere in my code.

Comment on Unknown warnings/errors

Replies are listed 'Best First'.
Re: Unknown warnings/errors by Tanktalus (Canon) on Jan 29, 2007 at 20:50 UTC
The way many compilers (including perl, it seems) handle multi-line statements is to treat the entire line either as the first or last line in the group (here, the last). You have a single statement spread over a bunch of lines, it's no wonder it gets confusing. The error is thus pointing to the first line there, since `/MSIE/` is short for `m/MSIE/` (see perlop). There are many improvements that should be made here, the least of which is to use proper if-then-else processing, and checking your values appropriately: `if (exists $ENV{HTTP_USER_AGENT} and $ENV{HTTP_USER_AGENT} =~ /MSIE/) { # handle MSIE case } else { # handle "other" case (could be Netscape, Firefox, Konqueror, Opera, + Nautilus, ...) }` [download] More major is to start using CGI instead of checking the environment, and to acknowledge more browsers are out there than you can shake a stick at, so just follow the standards and stop second-guessing the user.	[reply] [d/l] [select]
Re: Unknown warnings/errors by Joost (Canon) on Jan 29, 2007 at 20:51 UTC
m// is the "long hand" version of //, so the warning is probably referring to this: `($ENV{HTTP_USER_AGENT} =~ /MSIE/)` [download] If so, that would mean that $ENV{HTTP_USER_AGENT} isn't defined (i.e. you don't have an HTTP_USER_AGENT environment variable set. As a side note, you're probably better off using IE conditional comments to work around explorer's crappy CSS implementation. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^2: Unknown warnings/errors by kmullin5016 (Acolyte) on Jan 29, 2007 at 21:14 UTC
That makes sense. I'm usually running this from a web browser where it is set, but I'm running this in a test mode from a unix command line. Thank you.	[reply]
Re^3: Unknown warnings/errors by chargrill (Parson) on Jan 29, 2007 at 23:11 UTC
FYI, you can test ENV variables from the command line like so: `$ HTTP_USER_AGENT=MSIE perl myscript.cgi` [download] Or: `$ HTTP_USER_AGENT=FireFox perl myscript.cgi` [download] That is, put the environment variable name plus what value you want it to have, separated by an equals sign, immediately preceding your invocation of the script. Just a handy way to test things like that out. But I'll second Joost's advice (though not to the letter) and suggest dealing with goofy IE CSS implementations through plain CSS. --chargrill `s*lil; $=join'',sort split q; s;.;grr; &&s+(.(.)).+$2$1+; $; = qq-$_-;s,.,ahc,;$,.=chop for split q,,,reverse;print for($,,$;,$,$/)` [download]	[reply] [d/l] [select]
Re: Unknown warnings/errors by blazar (Canon) on Jan 30, 2007 at 11:05 UTC
`($ENV{HTTP_USER_AGENT} =~ /MSIE/) && do { # Internet Explorer $style{'body','font-size'}='10pt'; $style{'th','font-size'}='8pt'; $style{'td','font-size'}='6pt'; $style{'pre','font-size'}='10pt'; $titlebox_size='4'; 1; } \|\| do { # Netscape $style{'body','font-size'}='10pt'; $style{'th','font-size'}='10pt'; $style{'td','font-size'}='8pt'; $style{'pre','font-size'}='10pt'; $titlebox_size='5'; };` [download] On an unrelated basis to your actual problem, I do like to use short circuiting logical operators for flow control. But then the rule of a thumb is to use low precedence ones for this, and high precedence ones to operate on values (of course it actually doesn't make a difference here). However in this particular case they won't buy you anything over a regular, proper, `if`... `else`. Just so to let you know. Incidentally if you do so you won't incur in the "misplaced" warning line you're incurring into now.	[reply] [d/l] [select]
Re: Unknown warnings/errors by Anonymous Monk on Jan 30, 2007 at 10:26 UTC
If you use diagnostics, you'll get more use diagnostics; use warnings; ($ENV{HTTP_USER_AGENT} =~ /MSIE/) && do { warn 1}; __END__ Use of uninitialized value in pattern match (m//) at - line 4 (#1) (W uninitialized) An undefined value was used as if it were alread +y defined. It was interpreted as a "" or a 0, but maybe it was a mi +stake. To suppress this warning assign a defined value to your variables. To help you figure out what was undefined, perl tells you what ope +ration you used the undefined value in. Note, however, that perl optimiz +es your program and the operation displayed in the warning may not necessa +rily appear literally in your program. For example, "that $foo" is usually optimized into "that " . $foo, and the warning will refer +to the concatenation (.) operator, even though there is no . in your program. [download]	[reply] [d/l]