As described in perlretut (the regular expressions tutorial), you can use the character class \s to test for white space. As well, as long as you don't use the x modifier (for in lining comments), you can just use a space character in your code. In your case, however it's probably easier to test for characters that are not whitespace using \S:

for ("Hello", "   ", " x "  ) {
   print /\S/ ? "'$_': Fail\n" : "'$_': Pass\n";
}
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I tried but don't like this:


my $x = ""; 
if($x!~//g)  {

  print "\n There is true data\n";

}
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and this:


my $x = "      "; # just spaces
if($x!~/\s+/g)  {

  print "\n There is true data\n";

}
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Thanks

A couple of critiques for your expressions:
• Since you are only testing once, you do not need the g modifier.
• // will match everything. Hence $x!~// will always return false.
• /\s+/ will match if your string contains at least one space. Hence $x!~/\s+/ will return false if your string contains at least one space.
• Changing $x!~/\s+/ to $x!~/\S+/ will return true when the string does not contain at least one non-whitespace character, and hence will make your test work.
• You could use anchors (^ and $) and * to do what you intend as well with $x=~/^\s*$/. This translates as requiring that between the start (^) and end ($) there is exactly 0 or more (*) whitespace characters (\s).

I would suggest reading through perlretut to gain familiarity with this tool.

if (//g) makes no sense and it's a bug. It makes even less sense when negated. Get rid of the g.

if (defined $var or $var =~ /^\s+$/) {
    # $var is empty or contains only whitespace
}
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a variable can be empty (value is undef)

<nit>

The string could be undefined or defined and contain a zero-length string before we move on to containing only spaces or some other text.

$ perl -Mstrict -wE '
> sub grok
> {
>     my $str = shift;
>     say
>        defined $str
>        ? $str
>          ? qq{>$str<: defined and true}
>          : qq{>$str<: defined but not true}
>        : qq{>$str<: undefined};
> }
> 
> my $str;
> grok( $str );
> $str = q{};
> grok( $str );
> $str = q{   };
> grok( $str );
> $str .= q{ABC};
> grok( $str );'
Use of uninitialized value $str in concatenation (.) or string at -e l
+ine 5.
><: undefined
><: defined but not true
>   <: defined and true
>   ABC<: defined and true
$
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</nit>

Cheers,

JohnGG

but $var=""; and $var="data"; will both the in this IF, it doesn't work, I am trying to say if it is defined but empty move on.

I think this will do it:


if ( ($var =~ /^\s+$/) or ($var eq "") ){

print "\n All \n";

}else{
       print "\n Nothing \n";
       }
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I think this will do it:
<code> if ( ($var =~ /^\s+$/) or ($var eq "") ){ print "\n All \n"; }else{ print "\n Nothing \n"; }

So, your question becomes, how do I match strings that contain nothing but spaces? Translated into regexp speak, all you want to encounter between the beginning and end of a string is spaces. Translated to code, that is:

/\A *\z/
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