perl碱基计数的三种不同的方法，for循环+while循环+tr///

第一种方式，我们运用的for循环，然后用了if......else.......结构

for ($position=0;$position<length $DNA;++$position)
{
	$base=substr($DNA,$position,1);
	if ($base eq 'A')
	{
		$count_A=$count_A+1;
	}
	elsif ($base eq 'T')
	{
		$count_T=$count_T+1;
	}
	elsif ($base eq 'C')
	{
		$count_C=$count_C+1;
	}
	elsif ($base eq 'G')
	{
		$count_G=$count_G+1;
	}
	else
	{
		print "errorn"
	}
}

#然后依次读取字符串的元素，并对四种碱基的数量进行统计

while ($DNA=~/a/ig){$count_A++}
while ($DNA=~/c/ig){$count_C++}
while ($DNA=~/g/ig){$count_G++}
while ($DNA=~/T/ig){$count_T++}
while ($DNA=~/[^acgt]/ig){$e++}

F:&;perla.pl
please input the Path just like this f:perldata.txt
f:perldata.txt
A=40
T=17
C=27
G=24

F:&;

$count_A=($DNA=~tr/Aa//);
$count_T=($DNA=~tr/Tt//);
$count_G=($DNA=~tr/Gg//);
$count_C=($DNA=~tr/Cc//);

F:&;perla.pl
please input the Path just like this f:perldata.txt
f:perldata.txt
A=40
T=17
C=27
G=24

F:&;