I have XML files which I need to extract out certain values. So I wrote a code where it simply search for relevant text strings and extract out the values accordingly.

The problem is, how do I print the value of the formal_charge tag (e.g. -1)?

E.g. of my XML file: 
    <weight>18.998403205</weight>
    <name>fluoride</name>
    <smiles>[F-]</smiles>
    <accession>W00662</accession>
-<experimental_properties>
-<property>
    <kind>water_solubility</kind>
    <value>0.00169 mg/mL at 25 °C</value>
    <source/>
</property>
-<predicted_properties>    
-<property>
    <kind>formal_charge</kind>
    <value>-1</value>
    <source>ChemAxon</source>
</property>

[download]
Values I want is

weight (18.9984),

name (fluoride),

accession (W00662),

formal_charge (-1)

My code: 
sub load_files() {
  #get a list of all files in directory; ignore all files beginning wi
+th a . and other sub directories
  opendir(my $dh, $dirname) or die "can't opendir $dirname: $!";
  my @files = grep (/^[^\.]/ && -f "$dirname/$_", readdir($dh)); #only
+ keep those not beginning with '.' and are files  
  @files = sort(@files); #sort lexically, 'B' comes before 'a', so tha
+t output list is always in same order
  closedir $dh;
  
  my $numfiles = 0;

  foreach my $file (@files) { #loop through the files
    $numfiles++;
    
    my $accefound = 0;
    my $namefound = 0;
    my $monofound = 0;
    my $chargefound =0;
        
    open(my $file_fh, "< $dirname/$file") or die("$$: Error: failed to
+ open file $dirname/$file. $!\n");
    while(<$file_fh>) { #read each line of file
      if (/(<weight>)(.+)(<\/weight>)/ && !$monofound) { #if first enc
+ounter with the tag
        $monofound = $2;
        $monofound =~ s/^\s+//; #trim leading whitespace of string
        $monofound =~ s/\s+$//; #trim trailing whitespace of string
      }
    elsif (/(<name>)(.+)(<\/name>)/ && !$namefound) { #if first encoun
+ter with the tag
        $namefound = $2;
        $namefound =~ s/^\s+//; #trim leading whitespace of string
        $namefound =~ s/\s+$//; #trim trailing whitespace of string
      }
    
      elsif (/(<accession>)(.+)(<\/accession>)/ && !$accefound) { #if 
+first encounter with the tag (the tag might not be unique)
        $accefound = $2;
        $accefound =~ s/^\s+//; #trim leading whitespace of string
        $accefound =~ s/\s+$//; #trim trailing whitespace of string
      }
      
         elsif (/(<formal_charge>)(.+)(<\/formal_charge>)/ && !$charge
+found) { #if first encounter with the tag
        $chargefound = $2;
        $chargefound =~ s/^\s+//; #trim leading whitespace of string
        $chargefound =~ s/\s+$//; #trim trailing whitespace of string
      }

    }
    print "$monofound\t$namefound\t$accefound\t$chargefound\n";
 
    close($file_fh) or die("$$: Error: failed to close file $dirname/$
+file. $!\n");
  }
      
}



main();

[download]
What I got is: 
_OUTPUT DATA_
18.998403205    fluoride    W00662    0

[download]
The charge value is not reflecting -1, but it put "0" instead. I know it should match the word "value" , but in this case, there are many "value" tags in the file, so how do I actually match it to this value tag instead of incorrectly match other value tag? 
-<property>
    <kind>formal_charge</kind>
    <value>-1</value>  
    <source>ChemAxon</source>
</property>

[download]
I hope there is no need to involve any module and just searching relevant match string is sufficient?

In reply to Getting the value from XML file by hellohello1

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