Manipulating digits - perl

Question

This is a program which grabs lines which contains the $position AND $amino value in the first two columns.
Code:
#!/usr/bin/perl
my $id = $ARGV[0];
my $position = $ARGV[1]; # POSITION OF THE RESIDUE
my $amino= $ARGV[2]; #THREE LETTER AMINO ACID CODE IN CAPITALS
my #grabbed;
open (FILE, $id.$amino.$position.".hb2");
#CREATES AN ARRAY WITH ONLY THE VALUES FROM THE HB2 FILE. REMOVES THE HEADER OF THE FILE.
while (<FILE>) {
if (/^-/) {
push #grabbed, $_;
while (<FILE>) {
last if /^$/;
push #grabbed, $_;
}
}
}
close (FILE);
for ( #grabbed ) {
my #f = split;
if (( $f[2] == "-"."00".$position."-".$amino ) or ($f[0] == "-"."00".$position."-".$amino)) {
push #line, $id.$amino.$position, " ",$_;
}
}
print #line;
Partial input data :
-0007-ARG NH2 -0009-GLN OE1 3.24 SS 2 6.00 143.3 2.38 105.9 95.8 1 #CASE 1
-0008-GLU N -0008-GLU OE1 2.62 MS 0 -1.00 120.8 1.96 102.3 103.4 2
-0011-ILE N -0117-ARG O 2.87 MM 106 4.90 144.0 2.00 127.5 139.0 3
-0117-ARG N -0011-ILE O 2.75 MM 106 4.90 160.4 1.79 153.2 148.6 4 #CASE 2
-0016-SER N -0012-THR O 2.89 MM 4 6.00 156.2 1.95 149.8 154.8 5 #CASE 3
-0017-ALA N -0013-LEU O 3.10 MM 4 6.24 152.8 2.17 143.4 149.7 6
-0018-GLU N -0014-ARG O 3.04 MM 4 6.24 154.1 2.11 147.2 154.2 7
-0019-ILE N -0015-GLY O 2.90 MM 4 6.16 155.8 1.96 150.7 156.2 8
-0016-SER OG -0188-THR OG1 2.72 SS 172 5.92 172.0 1.73 98.9 99.6 9
-0188-THR OG1 -0016-SER OG 2.72 SS 172 5.92 163.7 1.75 116.4 115.1 10
Question :
In order to generalize the program I made the match as :
( $f[2] == "-"."00".$position."-".$amino ) or ($f[0] == "-"."00".$position."-".$amino)
The format is always four digits after "-" before $amino (-0188-THR). I suddenly realized that my code wouldnt work if the $position input is "one digit(like CASE 1)" or "three digit (like CASE 2, column 1)". Since I hard coded it as format as "-" followed by two zeros and THEN position, it has to always be two digit input to work.
I am stumped to generalize this code so that I could put in 1/2/3 digits. The remaining digits would always be replaced by zeros.

Answer 1

You can format the string using sprintf:
my $mstring = sprintf("-%04d-%s", $position, $amino);
if ( ($f[2] eq $mstring) or ($f[0] eq $mstring) ) {
# ...
}
Here, %04d adds 0's to the left of position to make it 4 digits long.

Answer 2

First, == operator in perl used only for comparing arithmetic expressions
To compare strings you should use eq operator
Second, to format strings from digits you can use sprintf function.
if ($f[2] eq "-".sprintf("%04d", $position)."-".$amino ...