perl は目的のファイルのパスを読み込み、対応するファイルを開きます。

AAAAAAAAAAAAAAGGGGGGGTTTTCCCCCCCC 
CCCCCGTCGTAGTAAAGTATGCAGTAGCVG 
CCCCCCCCCCGGGGGGGGGGAAAAAAAAAAAAAAATTTTTTAT 
AAACG 

# The following program is used to calculate the number of ATGCs in a segment of DNA sequence

#First define the number of four bases as 0
$count_A=0;
$count_T=0;
$count_C=0;
$count_G=0;
#First, we need to merge the sequence into one line

#First determine the path and filename of the file you want to process (on windows, follow this example)
#f:\\perl\\data.txt
print "please input the Path just like this f:\\\\perl\\\\data.txt\n";
chomp($dna_filename=<STDIN>);
# Open the file
open(DNAFILENAME,$dna_filename)||die("can not open the file!");
# Assign the file to an array
@DNA=<DNAFILENAME>;

# The following two steps are going to combine all the lines into one line and then remove all the white space characters
$DNA=join('',@DNA);
$DNA=~s/\s//g;

# Break the DNA into, and assign it to, an array
@DNA=split('',$DNA);

# Then read the elements of the array in turn and count the number of the four bases
foreach $base(@DNA)
{
 if ($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 "error\n"
 }
}
# Output the final result
print "A=$count_A\n";
print "T=$count_T\n";
print "C=$count_C\n";
print "G=$count_G\n";

F:\>perl\a.pl
Please input the Path just like this f:\\\perl\\\data.txt
f:\\perl\\\data.txt
error
A=40
T=17
C=27
G=24

F:\>

# The following program is used to calculate the number of ATGCs in a segment of DNA sequence

#First define the number of four bases as 0
$count_A=0;
$count_T=0;
$count_C=0;
$count_G=0;
#First, we need to merge the sequence into one line

#First determine the path and filename of the file you want to process (on windows, follow this example)
#f:\\perl\\data.txt
print "please input the Path just like this f:\\\\perl\\\\data.txt\n";
chomp($dna_filename=<STDIN>);
# Open the file
open(DNAFILENAME,$dna_filename)||die("can not open the file!");
# Assign the file to an array
@DNA=<DNAFILENAME>;

# The following two steps are going to combine all the lines into one line and then remove all the white space characters
$DNA=join('',@DNA);
$DNA=~s/\s//g;

# Then read the elements of the string in turn and count the number of the four bases
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 "error\n"
 }
}
# Output the final result
print "A=$count_A\n";
print "T=$count_T\n";
print "C=$count_C\n";
print "G=$count_G\n";

F:\>perl\a.pl
Please input the Path just like this f:\\\perl\\\data.txt
f:\\perl\\\data.txt
error
A=40
T=17
C=27
G=24

F:\>