my $var = ( $test =~ m/regex/ ) ? "true value" : "false value";
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my $var1;
my $var2;
if( $clause )
{
   $var1 = "blah";
   $var2 = "deblah";
}
else
{
   $var1 = "foo";
   $var2 = "bar";
}
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That said, only rarely is it a good design to have subroutines whose job is to communicate by setting global variables...

#!/usr/bin/perl5 -w
use strict;

my ($is_okay, $value);

sub return_okay {
   my $test_string = shift;
   my $private_result = ($test_string =~ /myregex/);
   return ($private_result);
}

sub return_okay2 {            # concise version
   return ($_[0] =~ /myregex/);
}

sub modify_okay {             # but see WARNING below
   # Called as: modify_okay($string, $result_flag)
   $_[1] = ($_[0] =~ /myregex/);
}

my @vals = qw(abcdefg myregex tuvwxyz);

print "Using a return value:\n";
foreach $value (@vals) {
   $is_okay = return_okay2($value);      ###
   if ($is_okay) {
      print "$value is okay.\n";
   }
   else {
      print "$value is not okay.\n";
   }
}

print "\nUsing a modified value:\n";
foreach $value (@vals) {
   modify_okay($value, $is_okay);        ###
   if ($is_okay) {
      print "$value is okay.\n";
   }
   else {
      print "$value is not okay.\n";
   }
}

# WARNING: the modify method can blow up on you
# Notice that the following line causes a fatal error 
# because of the attempt to modify a constant:

modify_okay("some string", 1);

print "And this never prints\n";
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Use return values. They don't choke trying to modify constants and (bonus) they are more clear. You have to look twice at the call to modify_okay() to figure out that the first variable is input but the second variable is being modified behind your back.

P.S. The above was intentionally verbose. With a little jiggering, the foreach loops can be condensed to:

for (@vals) {
   my $qualifier = return_okay2($_) ? "" : " not";
   print "$_ is$qualifier okay.\n";
}
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use strict;
sub test {
    if( $_[0] =~ /regex/ ) {
        $_[1] = "match";
    }
    else {
        $_[1] = "no match";
    }
}

my $bool;

test( "foo", $bool );
print "foo: $bool\n";

test( "regex", $bool );
print "regex: $bool\n";
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use strict;
{
    my $foo;
    sub setFoo{
        $foo = shift;
    }
    sub getFoo{
        return $foo;
    }
}
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my $myvariable;
my $this-variable;
$this-variable = 1 if $myvariable =~ /blah/;
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print "HEY!\n" if $this-variable;
print "NO!\n" if !$this-variable;
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