my $varString="George Washington was born on February 22, 1732";
print "Search string \"$varString\" for digits\n";
while ( $varString=~ m/(\d+)/g) {
print "Found digits: $1\n";
}
And the output will be:
Search string "George Washington was born on February 22, 1732" for digits
Found digits: 22
Found digits: 1732
Here the search pattern is “/(\d+)/”, “m” means match and ‘=~” tells perl to link to the string “$varString”. Lastly, “g” means do a global search on the string (from left to right). The search resulf, is stored in “$1”.
If we changed the code a little bit, without using the while loop and without using global search “g”::
my $varString="George Washington was born on February 22, 1732";
print "Search string \"$varString\" for digits\n";
$varString=~ m/(\d+)/;
print "Found digits: $1\n";
The outout will be:
Search string "George Washington was born on February 22, 1732" for digits
Found digits: 22
Perl find the first digits and stop and the resulf still store in $1.
Now, assuming that we forgot to use “~” and have the codes as the following:
my $varString="George Washington was born on February 22, 1732";
print "Search string \"$varString\" for digits\n";
$varString= m/(\d+)/;
print "Found digits: $1\n";
The output are:
Search string "George Washington was born on February 22, 1732" for digits
Use of uninitialized value in pattern match (m//) at ./perl_rex.pl line 8.
Use of uninitialized value in concatenation (.) or string at ./perl_rex.pl line 9.
Found digits:
The reason is when the “~” is omitted, perl is looking for a match of the regex in $_ and stores the search resulf to $varString.
Lets test it using the following codes:
my $varString="George Washington was born on February 22, 1732";
print "Search string \"$varString\" for digits\n";
$_="George Washington was born on February 22, 1732";
$varString= m/(\d+)/;
print "Found digits: $1\n";
print "Found digits: $varString\n";
And the output are:
Search string "George Washington was born on February 22, 1732" for digits
Found digits: 22
Found digits: 22
In fact, “m” is not reuested as long as you have used “~”, but using “~m” make the codes a bit easy to read, in my opions.
my $varString="George Washington was born on February 22, 1732";
print "Search string \"$varString\" for digits\n";
$varString=~ /(\d+)/;
print "Found digits: $1\n";
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