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Check if a string matches a regular expression

Display "ok" if "Hello" matches /[A-Z][a-z]+/
perl
print 'ok' if ('Hello' =~ /[A-Z][a-z]+/);

Check if a string matches with groups

Display "two" if "one two three" matches /one (.*) three/
perl
print $1 if "one two three"=~/^one (.*) three$/

Check if a string contains a match to a regular expression

Display "ok" if "abc 123 @#$" matches /\d+/
perl
print "ok" if ("abc 123 @#\$" =~ m/\d+/)

Loop through a string matching a regex and performing an action for each match

Create a list [fish1,cow3,boat4] when matching "(fish):1 sausage (cow):3 tree (boat):4" with regex /\((\w+)\):(\d+)/
perl
while ($text =~ /\((\w+)\):(\d+)/g) {
push @list, "$1$2"
}

Replace the first regex match in a string with a static string

Transform "Red Green Blue" into "R*d Green Blue" by replacing /e/ with "*"
perl
$text =~s/e/*/;

Replace all regex matches in a string with a static string

Transform "She sells sea shells" into "She X X shells" by replacing /se\w+/ with "X"
perl
$text = "She sells sea shells";
$text =~ s/se\w+/X/g;

Replace all regex matches in a string with a dynamic string

Transform "The {Quick} Brown {Fox}" into "The kciuQ Brown xoF" by reversing words in braces using the regex /\{(\w+)\}/.
perl
$text = "The {Quick} Brown {Fox}";
$text =~ s/\{(\w+)\}/reverse($1)/ge;