variable, variable name

sajithkutty · #1 (**permalink**) 04-08-2009

Hi,

I have this situation. I have a perl driver script that reads data from a data file. The data will be
1) function to call with arguments
2) error message to print if the function call fails.

My problem is, I need to be able to add variables in the messages in the data file. So my message could be something like,

$MsgCount... Msg to print when function call fails.

Where $MsgCount is calculated in my perl script before this message is read from file and printed.

When the message is read from the file, the complete message string is saved to a variable (say $x). But when i print the value of $x in my perl script i need the value of $MsgCount printed instead of the literal string.

I read somewhere i could something like ${$MsgCount} to accomplish this but it doesn't work. Could anyone fix my following program to cause the last print statement to ouput "value" please? Currently it prints out blank.

Code:

$day1date = "value";
print "day1date=$day1date\n";
$temp = "\$day1date";
print "*****temp = $temp\n";
print ${$temp};

Thanks in advance.
Sajith

sajithkutty · #2 (**permalink**) 04-09-2009

OK answering one's own post is not fun.

Anyway.
I got past the point where i was when i wrote my earlier post but now i'm stuck again.

the code (from my previous post) should have been

Code:

my $day1date = "value";
print "day1date=$day1date\n";
$temp = "day1date";
print "****temp = $temp\n";
print "----${$temp}\n";

This would work, UNLESS one uses strict, which I am. Now my test code looks like this...

Code:

  #!/usr/bin/perl
  use strict;
  my $string = "value of var1 is \$variable1 and that of var2 is $variable2";
  my $offset = 0;
  my ($char, $variablename);
  my $result=0;
  my $startloc=0;
  my $endloc=0;
  my $lenght=0;
  my $i = 1;
  my $variable1 = "firstvalue";
  my $variable2 = "secondvalue";
  while ($endloc != -1) {
    $char = '$';
    $startloc = index($string, $char, $offset);
    $offset = $startloc + 1;
    $char = ' ';
    $endloc = index($string, $char, $offset);
    if ($endloc == -1) { $lenght =  length($string) - $startloc; }
    else { $lenght = $endloc - $startloc; }
    $offset = $endloc + 1;
    $variablename = substr ($string, $startloc, $lenght);
   print "variablename = $variablename and its value is ${$variablename}.\n";
  }

But I get the error
Can' use string("$variable1") as a SCALAR ref while "strict refs" in use at .....

i also tried
no strict "refs";
just before
print "variablename = $variablename and its value is ${$variablename}.\n";

but the output I get is
variablename = $variable1 and its value is .
variablename = $variable2 and its value is .

I am hoping to get the following output
variablename = $variable1 and its value is firstvalue.
variablename = $variable2 and its value is secondvalue.

Please help

Thanks
Sajith

isha.dalwadi · #3 (**permalink**) 04-10-2009

Hey Sajith,

I am not sure about using the string as the variable name and getting the value. In your code i believe there is some mess happening with the references(addresses of the variables). But you can get the values of the variables using Hash with strict enable

.

Please see the below code.

#!/usr/bin/perl
use strict;
my $string = "value of var1 is \$no1 and that of var2 is \$no2";
my $offset = 0;
my ($char, $variablename);
my $result=0;
my $startloc=0;
my $endloc=0;
my $lenght=0;
my $i = 1;
my $no1 = "firstvalue";
my $no2 = "secondvalue";
my %hash;
$hash{'$no1'} = $no1;
$hash{'$no2'} = $no2;
while ($endloc != -1) {
$char = '$';
$startloc = index($string, $char, $offset);
$offset = $startloc + 1;
$char = ' ';
$endloc = index($string, $char, $offset);
if ($endloc == -1) { $lenght = length($string) - $startloc; }
else { $lenght = $endloc - $startloc; }
$offset = $endloc + 1;
$variablename = substr ($string, $startloc, $lenght);
#use Data:

umper;
#print Dumper{%hash};
print "variablename = $variablename and its value is $hash{$variablename}.\n";
}

Output:

D:\Perl_Scripts>perl temp.pl
variablename = $no1 and its value is firstvalue.
variablename = $no2 and its value is secondvalue.

Let me know this helped you or not?

Enjoy!!

Regards,
Isha

sajithkutty · #4 (**permalink**) 04-27-2009

Hi Isha,

Thanks for your reply.
THis script is quite close to what i actually need. Now my problem is in my actual script i will never know what variable forms a part of the string. So i cannot create hash references for the variables beforehand. I would also not like to limit the variables that can form a part of the string. Is there a way i can get rid of modify below statement such that it works for any variable in the complete script, not just $no1 and $no2.

my %hash;
$hash{'$no1'} = $no1;
$hash{'$no2'} = $no2;

Thanks again
Sajith

wecacuee · #5 (**permalink**) 08-06-2009

I know its late but you can use PadWalker.
warning:"I wouldn't recommend using PadWalker directly in production code"

Code:

perl -MData::Dumper -MPadWalker -e '
my $day1date = "1 June 2006";
print "$day1date=$day1date\n";
my $temp = "\$day1date"; 
my $pad = PadWalker::peek_my(0);
print "$temp=${$pad->{$temp}}\n";'

sajithkutty · #6 (**permalink**) 08-09-2009

Thanks wecacuee,

I tried your code and I got syntax error at line 1. I'm not sure if the single quotes at the end of 1st and last line are meant to be there. I tried couple of combinations but none worked. I finally tried

Code:

use PadWalker;
use strict;
my $day1date = "1 June 2006";
print "day1date=$day1date\n";
my $temp = "\$day1date";
print "temp = $temp\n";
my $pad = PadWalker::peek_my(0);
print "$temp=${$pad->{$temp}}\n";

This worked. Just what I needed.
I already have my code working without strict.
I'm not sure if I can have PadWalker installed on the UNIX environments I work on at my workplace. I'd love to include padwalker in my code, if I can.
Why exactly do you say one shouldn't use it in prod?

Thanks again.
Sajith

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