Regex : Using expressions

This is the /e modifier

Example: make HTML tags upper case

# ( ) - capture the text
# .*? - match the least amount of text, i.e. an HTML tag
# uc ($1) - make the matches text uppercase
# gxe - g is global replace
# gxe - x is allow whitespace and comments
# gxe - the bit on the right is an expressions to be evaluates

$html =~ s# ( < .*? > ) # print uc($1) #gxe ;

Example : find hi byte characters

# find hi-byte characters in HTML
# - and keep a record of all the hi byte chars found in %found
my %found ;

sub find {
 my ($char) = @_ ;
 $found{ $chars } ++; ## keep a record
 return '[' . ord( $chars ) . ']';
 }

## this will find euro and £ symbols, but not €
## \x80 is hex (ascii char 128)
## \x80-\xffff is a range - if the file is utf8, it will match hi bytes chars as well
## gxe - expression, whitespace, and global replace
$html =~ s# [\x80-\xffff] # &find( $1 ) #gxe;