Newbie Q re: Undefined Value and "only used once" warnings

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

An experienced pgmmr, I'm totally new to Perl, and appreciate any guidance you might provide.

I have 3 issues which I've been wrestling with for over a full day, and cannot find the answers:

At "Error1" below -- Whenever I run the scipt, I get the msg,

Can't call method "My" on an undefined value at G:\PERLCODE\NEWSCR~1.C
+GI line 23."
[download]

But that's what I'm trying to do . . . define the value. And, without MAIN::, I get the error,

global symbol $LogMsg requires explicit package name".
[download]

At "Error2" -- I had understood that $^W = 0 would turn off the warnings, but it doesn't. Did I miss something?

Finally, at Error3 -- Without the "my $temp = $MAIN::Log;" statement, I get warnings about "$MAIN::Log only used once", but it's assigned a value at the beginning of MAIN, and then used in the write sub . . .

Thanks in advance for your help!!!

#!  perl   -w
use strict;
use diagnostics;

use Time::localtime;
use Config::IniFiles;


MAIN:{
my $DirPath = 'A:\\TempIMS_Work\\Listings\\';
my $Logfile = 'DRS_FileModify.log';
my $StdErrfile = 'DRS_FileModify_StdErr.log';

my $Log = $DirPath.$Logfile;
my $StdErr = $DirPath . $StdErrfile;


# Just to get around warning of "Only Used Once"
my $dummystmt = $Log . $StdErr;


#Error1
My $MAIN::LogMsg = "\n\n" . &getDateTime() . "\ - Starting Processing\
+n\n";

# Start the log and StdErrLog
 &writeLog();
 &writeStdErr();

# Ensure the log path exists

    opendir (Dir, $MAIN::DirPath)
        or die "\n\nCannot open the path for the processing log: $MAIN
+::DirPath -- $!\n";
    closedir(Dir);

# Loop
# Process each DRS file -- Call processDRS_File
# EndLoop

# If error, FTP the errmsg
#        if FTP failure, write to logs

# if success, write o.k. msg to logs

#EOJ
}




# Subroutines and Functions

sub getDateTime {;
    my $tm = localtime(time);
    my $ampm = "am";
    my $tempHour = undef;

    if ($tm->hour > 12)
          {$tempHour = $tm->hour - 12;
          $ampm = "pm";
          }
     else {
          $tempHour = $tm->hour;
     };

    return (sprintf("%02d/%02d/%02d  %02d:%02d %02s",
            $tm->mon+1, $tm->mday, substr($tm->year + 1900, 2, 2),
            $tempHour, $tm->min, $ampm)
            );
};

sub writeLog() {
#Error2
#  $^W = 0;
     open LOGFILE, '>>', "$MAIN::Log"
        or die "ERROR: Cannot open Log file: $!";
#    $^W = 1;
#Error3
#  my $temp = $MAIN::Log;
     print LOGFILE $MAIN::LogMsg;
  close LOGFILE;
};

sub writeStdErr() {
     open STDERRFILE, '>>', "$MAIN::StdErr"
        or die "ERROR: Cannot open StdErr file: $!";
    my $temp = $MAIN::StdErr;
     print STDERRFILE $MAIN::LogMsg;
  close STDERRFILE;
};
[download]

Comment on Newbie Q re: Undefined Value and "only used once" warnings Select or Download Code

Replies are listed 'Best First'.
Re: Newbie Q re: Undefined Value and "only used once" warnings by ambrus (Abbot) on May 15, 2004 at 18:31 UTC
Yes, perl is case sensitive, so my instead of My. About `$^W= 0;`, it runs at run-time, so it won't affect the "once" warning, which is generated at conpile-time. To remedy, either put the $^W in a begin-block (like `BEGIN {$^W= 0;}`), or with perl >=5.6, use the warnings pragma: `no warnings "once";` turns off just the "once" warnings, and it's scoped lexically to the block, so you can write `{no warnings;` SOME CODE THAT WOULD GIVE A WARNING `}` and hush, the effect is gone when you close the block. (`no warnings` affects both compile-time and run-time warnings.) Corrected typo s/rub-time/run-time/ noted by arden. Thx.	[reply] [d/l] [select]
Re: Newbie Q re: Undefined Value and "only used once" warnings by ambrus (Abbot) on May 15, 2004 at 18:48 UTC
About the third error. Unike some cases with the "only used once" warning, Perl is right here. You've messed up scoping rules, the `$MAIN::Log` you're trying to access is not the same as the `$Log` variable above. `$MAIN::Log` is the `$Log` variable of the MAIN package, which can not be your `Log` for two reasons. Firstly, you declare that `$Log` with `my`, so it's a lexical variable, which does not belong to any package, instead, it belongs to the innermost lexical scope in which the declaration is, which is in this case the brace-block labeled MAIN. If you declare a `my` variable in that block, you can use its name only in that block. Secondly, there's no MAIN package here. The loop label MAIN does not create a package, you have to use the `package` statement for that. (You might be thinking that you are in package MAIN by default, in the absencse of pkg declarations. Not, that's package `main` in lc.) There are two ways you could correct this. The first is that you use a lexical variable. You say `my $Log` before the opening of the MAIN loop, that way it is valid in the whole script (which is by itself a scope, although the largest one), and then you can refer it with `$Log`, that is, without a package name later. The second is that you really use a global variable. In this case, you first have to say `package MAIN` somewhere, or just write `main` instead, which is the default package. Then, you change the declaration to `our $Log= ...` at the assignment, and wow, it's a global variable you can access as `$MAIN::log` or `$main::log` depending in what package you've just set. The first solution is probably appropriate here, I've just written the second so that you know what `$MAIN::Log` really means here. (Someone knowing pm please recommend some good tutorial about my and our in this thread. Thx.)	[reply] [d/l] [select]
Re^2: Newbie Q re: Undefined Value and "only used once" warnings by Nkuvu (Priest) on May 15, 2004 at 19:17 UTC
From Tutorials, I found Ovid's 'our' is not 'my'.	[reply]
Re: Newbie Q re: Undefined Value and "only used once" warnings by Nkuvu (Priest) on May 15, 2004 at 19:11 UTC
On a completely different note, I noticed that you're creating your own getDateTime function. It looks like you're duplicating effort. If you replace the `use Time::localtime` line with `use POSIX qw(strftime)`, you can use the following line for formatting the time: `strftime ("%D %l:%M %p", localtime)` (note that that's a lowercase L for the hour) which prints out exactly what you have for getDateTime. Well, really close, I condensed two spaces between the date and the hour into one space. The format string I built from the formats given in `man strftime` -- but if you aren't running on a Un*x (or OS X) box you can Google for the manpages easily enough. There may very well be reasons you're not using `strftime`, I just wanted to make sure you're aware of the option.	[reply] [d/l] [select]
Re: Newbie Q re: Undefined Value and "only used once" warnings by exussum0 (Vicar) on May 15, 2004 at 17:42 UTC
`My $MAIN::LogMsg = "\n\n" . &getDateTime() . "\ - Starting Processing\` [download] It's my, not My. Humma la beeba la seeba la booba la Humma la beeba la seeba la bop	[reply] [d/l]
Re: Newbie Q re: Undefined Value and "only used once" warnings by arden (Curate) on May 15, 2004 at 18:33 UTC
As sporty pointed out, Perl is very much so case sensitive! my is a built-in Perl function, whereas My doesn't have any special meaning, so Perl assumes that it's a custom method which you've neglected to include the code for. As for warnings, if you really want to get rid of all warnings, then add `no warnings;` at the beginning of your code. Of course, if you have warnings turned off and are having problems, you're not likely to find a sympathetic crowd here at the Monastery. :) - - arden.	[reply] [d/l]
Re: Newbie Q re: Undefined Value and "only used once" warnings by Errto (Vicar) on May 15, 2004 at 19:31 UTC
Another issue that the above posts touch on is your use of package variables. When you refer to `$MAIN::Log`, that is being treated as the variable called `$Log` in the package `MAIN`. This has nothing to do with your declaration `MAIN:`, which is merely creating a line label that you could use in a `next` or `last` statement. If you really want a package, you should declare it with `package MAIN;`. But I think a better idea, would be to put your decalarations like this: `my $Log; my $LogMsg; my $StdErr;` [download] at the very top of your program outside any blocks. Then remove all the MAIN:: references everywhere you have them now.	[reply] [d/l] [select]
Re: Re: Newbie Q re: Undefined Value and "only used once" warnings by mikeatrcn (Acolyte) on May 15, 2004 at 20:28 UTC
Thank you all!!!!!!!!!! These are all very valid points, well explained, and VERY much appreciated, as I learn Perl while developing an application under time constraints at work!	[reply]