Need help with loop syntax errors

[Todd Chester]

Hi All,

I am trying to write myself a demonstration of differenct types of word subsitutions in two differnt types of loops. Problem: I can't figure out all the syntax errors. Any help would be greatly approciated.

#!/usr/bin/perl

# Demonstrate different loops for use with string substitutions

use strict;
use warnings;
# use diagnostics;

my $NewRev = "\tabc\tkis17.1.33en_12345.exe<h href";
my $RedirectUrl;

s/.*kis17/17/, s/.exe//, s/en_/./ for $NewRev = $RedirectUrl;
print "for at the end: \$RedirectUrl = <$RedirectUrl>\n\n";

$NewRev = $RedirectUrl =~ s/.*kis17/17/r =~ s/.exe//r =~ s/en_/./r ;
print "run on line: \$RedirectUrl = <$RedirectUrl>\n\n";

for ($NewRev = $RedirectUrl) {s/.*kis17/17/; s/.exe//; s/en_//; }
print "for at the start: \$RedirectUrl = <$RedirectUrl>\n\n";
END

Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.pl line 12.
Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.pl line 12.
Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.pl line 12.
Use of uninitialized value $RedirectUrl in concatenation (.) or string at ./LeftToRight.pl line 13.
for at the end: $RedirectUrl = <>

Use of uninitialized value $RedirectUrl in substitution (s///) at ./LeftToRight.pl line 15.
Use of uninitialized value $RedirectUrl in substitution (s///) at ./LeftToRight.pl line 15.
Use of uninitialized value $RedirectUrl in substitution (s///) at ./LeftToRight.pl line 15.
Use of uninitialized value $RedirectUrl in concatenation (.) or string at ./LeftToRight.pl line 16.
run on line: $RedirectUrl = <>

Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.pl line 18.
Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.pl line 18.
Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.pl line 18.
Use of uninitialized value $RedirectUrl in concatenation (.) or string at ./LeftToRight.pl line 19.
for at the start: $RedirectUrl = <>

[Marshall]

I made a few corrections for you below. "diagnostics" just gives a more verbose explanation of error messages. I don't use it.

#!/usr/bin/perl

# Demonstrate different loops for use with string substitutions

use strict;
use warnings;
# use diagnostics;

my $NewRev = "\tabc\tkis17.1.33en_12345.exe<h href";
my $RedirectUrl;

s/.*kis17/17/, s/.exe//, s/en_/./ for $NewRev; #you assigned null to $
+NewRev
print "for at the end: \$NewRev = <$NewRev>\n\n";

$NewRev = "\tabc\tkis17.1.33en_12345.exe<h href"; #set back to origina
+l
$RedirectUrl = $NewRev =~ s/.*kis17/17/r =~ s/.exe//r =~ s/en_/./r ; 
print "run on line: \$RedirectUrl = <$RedirectUrl>\n"; #modified
print "run on line: \$NewRev = <$NewRev>\n\n";         #not modified

$NewRev = "\tabc\tkis17.1.33en_12345.exe<h href"; #set back to origina
+l
for ($NewRev) {s/.*kis17/17/; s/.exe//; s/en_//; }
print "for at the start: \$NewRev = <$NewRev>\n\n";

$NewRev = "\tabc\tkis17.1.33en_12345.exe<h href"; #set back to origina
+l
for ($NewRev)  #white spaces consumes no Mips! why so compact?
{
   s/.*kis17/17/;   #all 3 statements modify $NewRev
   s/.exe//; 
   s/en_//; 
}
print "for at the start: \$NewRev = <$NewRev>\n\n";


__END__

Need __END__ not just END
But of course __END__ is optional, just use it like this when you
want to put something in the code like an example printout

Prints:
for at the end: $NewRev = <17.1.33.12345<h href>

run on line: $RedirectUrl = <17.1.33.12345<h href>
run on line: $NewRev = <    abc    kis17.1.33en_12345.exe<h href>

for at the start: $NewRev = <17.1.3312345<h href>

for at the start: $NewRev = <17.1.3312345<h href>

[Todd Chester]

Thank you!

I am going to chew on this until I understand it and then post it back. Sometimes and example is worth a thousand words!

What do you mean "you assigned null to $NewRev"?

[Marshall]

You had

my $NewRev = "\tabc\tkis17.1.33en_12345.exe<h href";
my $RedirectUrl;
## and then... for($NewRev = $RedirectUrl);

That assigns $RedirectUrl to $NewRev and then uses that result in the for loop. Since $RedirectUrl is null undefined (the simple my $RedirectUrl; statement). That is the source of one of your "use of uninitiatized value warnings". Note that the code keeps going after a warning. A warning is not considered "fatal". An "error" will stop the program.

Make Sense?

Update: I don't want to quibble about definitions of definitions of "warning, syntax error" or whatever. You have some code that runs now without any warnings. Continue on with your experimentation...I commend you for that effort.

[Anonymous Monk]

warnings are warnings not syntax errors, if they're unclear, use diagnostics;

also, it doesn't make sense to keep writing  $NewRev = $RedirectUrl

[Todd Chester]

Thanks for the tip on the wording. This is what I thought I was using: "In computer science, the syntax of a computer language is the set of rules that defines the combinations of symbols that are considered to be a correctly structured document or fragment in that language."
Wikipedia Syntax
I will come up to speed eventually!

I uncommented out "use diagnostics". I don't mean to be dense, but, I still can't figure out what I am doing wrong? What is the correct structure?

$ ./LeftToRight.pl
Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.
+pl line
    12 (#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 will try to tell y
+ou
    the name of the variable (if any) that was undefined.  In some cas
+es
    it cannot do this, so it also tells you what operation you used th
+e
    undefined value in.  Note, however, that perl optimizes your progr
+am
    anid the operation displayed in the warning may not necessarily ap
+pear
    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.
    
Use of uninitialized value $RedirectUrl in concatenation (.) or string
+ at
    ./LeftToRight.pl line 13 (#1)
for at the end: $RedirectUrl = <>

Use of uninitialized value $RedirectUrl in substitution (s///) at
    ./LeftToRight.pl line 15 (#1)
Use of uninitialized value $RedirectUrl in concatenation (.) or string
+ at
    ./LeftToRight.pl line 16 (#1)
run on line: $RedirectUrl = <>

Use of uninitialized value $_ in substitution (s///) at ./LeftToRight.
+pl line
    18 (#1)
Use of uninitialized value $RedirectUrl in concatenation (.) or string
+ at
    ./LeftToRight.pl line 19 (#1)
for at the start: $RedirectUrl = <>

[Anonymous Monk]

blah blah blah

There is no problem with the structure, there is no syntax problem, no syntax error, like I said, the warning you get is a warning, its not a syntax error, and its telling you what the problem is, and diagnostics telling you in more than one line

What its saying is that $RedirectUrl is uninitialized, it doesn't have a value, its empty, its undef, its value is undef, there is nothing thiere, its an empty bucket full of space, you wont find find en_ or .exe or anything in the bucket, its empty, there is nothing inside to find but air, you can keep searching the empty bucket, it will continue to be empty,

perl warned you, and you're like, man perl is telling me this bucket is empty, how am I supposed to hold the bucket?

an empty bucket is empty, if you want it to have stuff inside, put stuff in it, dont put empty in it

Maybe you'd like to stop writing   $NewRev = $RedirectUrl ?

[Todd Chester]

I keep "$NewRev" as I am trying to demonstrate several different methods of doing the same thing. Erase and reuse.