testing if a value is empty

[donny750]

hello,

I want to test if the value writing in the prompt is not empty;
i've use astructure control : unless but if i write no value and i press enter, in my file i found this
SYS=
or if no value is written , normally i can't exit from the structure control.
my code

#!/usr/bin/perl -w

use strict;

open FILE, ">./fic.cfg";
print "SYS Value = \n";
my $SYS=<stdin>;
unless ($SYS)
{
print "SYS Value =\n";
my $SYS=<stdin>;
}
print FILE "SYS=$SYS\n";

thanks

 

[Kirsle]

There's a few things you can do depending on what you mean by "empty":

# If empty means not defined
my $var;
# or: my $var = undef;
if (defined $var) {
   print "var was defined\n";
}
else {
   print "var wasn't defined\n";
}

# if empty means blank value
my $var = '';

# you can check with length
if (length $var == 0) {

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[Kirsle]

On another note, 'defined' will return true if the variable has a blank value, ie

my $var = '';
if (defined $var) # should return true

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[KevinADC]

you probably want something more like this:

#!/usr/bin/perl -w
use strict;
my $SYS = undef;
while (!$SYS) {
   print "SYS Value = \n";
   chomp($SYS=<STDIN>);
}
open FILE, ">./fic.cfg";
print FILE "SYS=$SYS\n";
close (FILE);

- Kevin, perl coder unexceptional!

 

[donny750]

i've this script

if ($valid ne "o")
{


do {
    print $_[1]."[".$_[0]."]";
    $_[0] = <stdin>;
    print "\n"; 	
    chomp($_[0]);
    
   } while (! ($_[0]));

}
else
{
print $_[1]."[".$_[0]."]";
    
   $_[0] = <stdin>;
   
   if (! ($_[0]))
	{ 
	$_[0] = $old; 
	} 
    print "\n";

    chomp($_[0]);

}

this part of the script don't execute as i want

else
{
print $_[1]."[".$_[0]."]";
    
   $_[0] = <stdin>;
   
   if (! ($_[0]))
	{ 
	$_[0] = $old; 
	} 
    print "\n";

    chomp($_[0]);

}

what i want is :
if there no values are taking in the prompt (<stdin>);i want
$_[0] equal to $old;
But when i run the script,if i take no value , i've not the old value;
My test seem not run good

(! ($_[0]))

??

 

[donny750]

i've resolve this
with something like this

$_[0] = <stdin>;
  
   $value = $_[0];
   
   if ((length($new)-1) == 0)
	{ 

	 $_[0] = $old; 

	}

 

[donny750]

heu
this is good

$_[0] = <stdin>;
  
   $value1 = $_[0];
   
   if ((length($value1)-1) == 0)
    { 

     $_[0] = $old; 

    }

 

[Kirsle]

The reason $_[0] has a length of 1 is because when you hit enter in <STDIN>, it puts a newline character (\n) at the end of whatever you typed. If you typed nothing, then it will return just "\n"

So chomp the variable. Chomp gets rid of newline characters from the end of a variable.

$_[0] = <stdin>;
chomp $_[0];

or even better

chomp ($_[0] = <STDIN>);

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