Transcript Document
Regular Expression
A regular expression is a template
that either matches or doesn’t
match a given string.
Regular Expression: simple
patterns
$_ = “yabba dabba”;
#pattern match return a true or false
if($_ =~ /abba/)
{
print “It matched!\n”
}
Regular Expression:
Dot (.): matches any single character(but not \n)
Backslash(\): escape from special character
/3.14159/ matches 3.14159, 3214159, 3=14159
Star (*): matches zero or more of preceding item
/fred*/ matches fre, fred, fredddd.
Plus(+): matches one or more of preceding item
/3\.14159/ matches 3.14159 only
/fred+/ matches fred,fredddd but not fre
Square brackets([ ]) matches any single character from within the class
[a-zA-Z] matches any letter [0-9] matches any number
Regular Expression:
Parentheses( “()”) may be used for grouping
Vertical bar (|) matches either the left side or and right side
$test = “apple banana”;
if($test =~/(ap*le)\s+(banana)/)
{
print “first group:$1 and second group:$2\n”;
}
$test1 = “1abc”;
$test 2 = “2abc”;
if(($test1 =~/(1|2)abc/)and($test2 =~/(1|2)abc/))
{
print “test1 and test2 both match to our pattern”;
}
Anchors (^) matches the beginning of a string(line) and ($) match the end of a string (line)
Regular Expression:
substitutions
Perl’s s/// substitution operator does the
‘search and replace’
$line = “He is out with Barney. He is really happy!”;
$line =~ s/Barney/Fred/; #He is out with Fred. He is really
happy!
$line =~ s/Barney/Wilma/;#He is out with Fred. He is really
happy! (nothing happens as search failed)
$line =~ s/He/She/; #She is out with Fred. He is really happy!
$line = “He is out with Fred. He is really happy”
$line =~ s/He/She/g; #She is out with Fred. She is really
happy!
Regular Expression:
translations
The "tr///" operator performs a substitution on
the individual characters ina string.
Examples:
$x =~ tr/a/b/;
# Replace each "a" with a "b".
$x =~ tr/ /_/;
# Convert spaces to underlines.
$x =~ tr/aeiou/AEIOU/; # Capitalise vowels.
$x =~ tr/0-9/QERTYUIOPX/; # Digits to letters.
$x =~ tr/A-Z/a-z/;
# Convert to lowercase.
Regular Expression: split &
join
Split breaks up a string according to a
separator.
$line = “abc:def:g:h”;
@fields = split(/:/,$line) #(‘abc’,’def’,’g’,h’)
Join glues together a bunch of pieces to
make a string.
$new_line = join(“:”,@fields) #“abc:def:g:h”
Regular Expression
Write a function that transcribe DNA to
RNA
Write a function that do reverse
complement of strand of DNA.
Test these two functions and print
output into a report file