PERL -- Regex incl all hash keys (sorted) + deleting empty fields from $_ in file read -

i'm working on program , have couple of questions, hope can help:

first need access file , retrieve specific information according index obtained previous step, in indexes retrieve found , store in hash.

i've been looking way include array elements in regex can use in file search, haven´t been able make work. i've found way works:

my @atoms = (); $natoms=0;  foreach $atomi (keys %{$atome}){ push (@atoms,$atomi); $natoms++; } @atoms = sort {$b cmp $a} @atoms; 

and use regex way:

while (<in_lig>){ if (!$natoms) {last;} ...... if ($_ =~ m/^\s*$atoms[$natoms-1]\s+/){     $natoms--;       ..... } 

is there way create regex expression include hash keys? numeric , must sorted. keys refer line index in in_lig, content this:

8 c5          9.9153    2.3814   -8.6988 c.ar      1 mlk        -0.1500  

the key found in column 0 (8). have added ^ , \s+ make sure refers first column.

my second problem input files not identical , make contain white spaces before index, when create array $_ column0 = " " instead of column0=8

i don't understand why "empty column" not eliminated on split command , i'm having trouble remove it. have done:

@info = split (/[\s]+/,$_);  if ($info[0] eq " ") {splice (@info, 0,1);} # tried $info[0] =~ m/\s+/ 

and when print array @info this:

array:   array: 8  array: c5  array: 9.9153  array: 2.3814  ..... 

how can rid of empty column?

many merche

there special form of split remove both leading , trailing spaces. looks this, try it:

my $line = '  begins     spaces  , ends     spaces    '; @tokens = split ' ', $line; # prints |begins:with:spaces:and:ends:with:spaces| print "|", join(':', @tokens), "|\n"; 

see documentation split @ http://p3rl.org/split (or perldoc split)

also, first part of program might simpler as:

my @atoms = sort {$b cmp $a} keys %$atome; $natoms = @atoms; 

but, ultimate goal atoms? if want verify atoms you're given indeed in file, don't need sort them, nor count them:

my @atoms = keys %$atome; while (<in_lig>){     # atom id on line     ($atom_id) = split ' ';     # atom id in array of atom ids looking     if (grep { /$atom_id/ } @atoms) {         # line of file has atom in array: $atom_id     } }