Re: [PLUG] Re: plug Digest, Vol 16, Issue 31

[bergman@merctech.com]

In the message dated: Mon, 27 Mar 2006 11:16:47 EST,
The pithy ruminations from Eric on 
<Re: [PLUG] Re: plug Digest, Vol 16, Issue 31> were:
=> Quoting Jeff Watson <redgibson@gmail.com>:
=> 
=> > I am having an issue with this part of my perl script.
=> > 
=> > # eat output file, chop all lines but the load lines
=> > my $output = "c:\\TEST.out";
=> > 
=> > if($ARGV[0]) {
=> >   print $ARGV[0] . "\n";
=> >   my $input = $ARGV[0];
       ^^^

=> >   print $input
=> > }
=> > else {
=> >   print "BAD INPUT: Missing parse target filename!";

I'd change this to:
	
	print "BAD INPUT: Missing parse target filename!\n";

=> >   exit(0);
=> > }
=> > 
=> > # ASSUME $input = C:\test.chm' !!
=> > #open(MYFILE, 'c:\test.chm');                     # THIS WORKS!!!
=> > open(MYFILE, $input);                               # THIS FAILES!! :-/
=> > 
=> > while(<MYFILE>) #Drops out on this line becuase the file is not able to be
=> > opened?
=> > .......
=> > 
=> > 
=> >             -Jeff Watson
=> >             -RedGibson@gmail.com
=> 
=> Jeff:
=> 
=> I always code the open statements as:
=> 
=> open MYFILE, "<$input" or die "Cannot open file $input" ;

Good idea. I'd suggest:
	open MYFILE, "<$input" or die "Cannot open file $input: $!" ;	
adding "$!" will give you the error message as returned by "open()"--this lets 
you distinguish between things like "permission denied" and "no such file or 
directory".

If you do make this change, and run the script, the error message _will_ tell 
you (implicitly) what's going wrong. For example:
	./myscript fubar	# run the script, specifying "fubar" as the
				# name of the input filename
	fubar
	Cannot open file : No such file or directory at myscript line 16.

Look closely...note that the filename is missing in the error statement...
Now, wasn't that filename assigned to $input within the decision block 
following the test "if($ARGV[0])"? Yes, there was an assignment of "fubar" to
$input, and the single line of text (fubar) shows that...so, why was that 
variable blank when the open() statement was executed?

Hint...how was the $input variable defined?


[SPOILER FOLLOWS]



































According to the camel book (2nd ed., p. 108):
	A _my_ or a _local_ declares the listed variables (in the case of
	_my_, or the values of the listed global variables (in the case of
	_local_), to be confined to the enclosing block...

So, you're assigning a value to $input, but that value only persists within the 
block, and it disappears by the time you want to use $input in the open() 
statement.

Mark
 
=> so when it cannot open the file it will tell you.
=> 
=> I don't use perl in Windows a lot but I'd try double back-slash '\\' 
=> in the file name because perl may be seeing the single backslash as 
=> an escape for the next char when you pass it to the open function.
=> 
=> Eric
=> 
=>
-----
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