“Hello world” =~/world/ -> evaluates to true
“Helllo world”!~/world/ -> evaluates to false
$word= “world”
$_=”Hello world”
print “It matches “ if $world
“Hello world”=~m!world!
“Hello world”=~m{world}
Meta characters
{} [] () ^ $ . * + ? \
Escape sequences
\t \n \033 \x1B
Anchor meta characters
$ = end
^ = beginning
Character classes
/[b,c,r]at/ - matches bat, cat and rat
/yes/i - here i denote case insensivity
Special charactors for character classes are -]\^$
‘-‘ rage operator
/item[0-9]/
If – is first/last in the class it is treated normally
Perl abbreviation for common char classes
\d – digit [0-9]
\s – whitespaces [\ \t\n\t\f]
\w – wordchar [0-9a-zA-Z_]
\D – negate \d
\S – negate \s
\W – negate \w
. – matches any character but “\n”
Word anchor - \b
$x = “Housecat catenates house & cat”
$x = ~/\bcat/
$x = ~/cat\b/
$x = ~/\bcat\b/
Alternation meta character |
“cats and dogs”=~/cats|dogs/
Grouping hierarchical matching…
Grouping meta characters ‘()’
/house(cat(s|))/
Extracting matches
$time =~/(\d\d):(\d\d):(\d\d)
$hour=$1
$min = $2
$sec = $3
/(ab(cd|ef))((gi)|j)/
$1 $2 $3$4
Bock referencing (\1,\2…)
/(\w\w\w)\s\1/ - matches words like “the the”
Matching repetition
a? – 0 or 1 a’s
a* - 0 or more a’s
a+ - 1 or more a’s
a{n,m} – least n not more than m
a{n,} – at least n
a{n} – exactly n
xx/xx/o – row substitution
xx/xx/g – global
Search & replace
s/regex/replacement/modifiers
$y = “’quoted modifiers’”
$y=~ s/^’(.*)’$/$1/
$x=”I batted 4 for 4”
$x =~ s/4/four/g
#resulted in I batted four for four
s///, s!!!, s{}{}
s{}//, s’’’
The splitter operator
$x = “Calving and Hobbes”
@word = split/\s+/,$x
#$word[0]=’calving’
#$word[1]=’and’
#$word[2]=’Hobbes’
