Regular Expression for alphanumeric and underscores

Question

I would like to have a regular expression that checks if a string contains only upper and lowercase letters, numbers, and underscores.

Answer 1

The following regex matches alphanumeric characters and underscore:

^[a-zA-Z0-9_]+$

For example, in Perl:

#!/usr/bin/perl -w

my $arg1 = $ARGV[0];

# check that the string contains *only* one or more alphanumeric chars or underscores
if ($arg1 !~ /^[a-zA-Z0-9_]+$/) {
  print "Failed.\n";
} else {
    print "Success.\n";
}