use warnings;
use strict;

while (<DATA>) {
    if (/(\w+)=\w+ (\w+)=/) {
        my $diff = hex($2) - hex($1);
        printf "0x%x %d\n", $diff, $diff;
    }
}

__DATA__
0x405d75=inst1 0x405d7a=inst2
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This is the piece of code that i wrote to extract the above mentioned hexadecimal values and now i want to subtract the $valu2 with $value1 and print it in the same output file F2. I am not sure how to subtract these 2 values and print the result in hexadecimal and also in integer

#!usr/bin/perl

open (FILE1, "<file_hex.txt") or die "can't read the file";
open (FILE2, ">output_log.txt") or die "cant write into the file";

while (<FILE1>) {
        if($_ =~ (/(^\=\>\s+)(0x[0-9a-f]+){1,10}(.*)/)) {
        $value1= $2;    
        print FILE2 $value1."=inst1 \n";
    }
    elsif($_ =~ (/(^\s+)(0x[0-9a-f]+){1,10}(.*)/)) {
        $value2=$2;
        print FILE2 $value2."=inst2 \n";
    }          
}
close (FILE1);
close (FILE2);
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Thanks

The basic technique for extraction and substraction was shown by toolic. I don't know why you haven't used this nor why you seem to be asking exactly the same question in response to his reply: he's shown you how to extract the data, do the subtraction and output the result in the formats requested. Perhaps you should provide expected output to clarify your question.

Now that we can see the format of your input data, I can show you how to read pairs of lines.

#!/usr/bin/env perl

use strict;
use warnings;

{
    local $/ = "inst2\n";

    while (<DATA>) {
        /^(\w+)=\w+\s+(\w+)/;
        printf "%#x %1\$d\n" => hex($2) - hex $1;
    }
} 

__DATA__
0x405d75=inst1
0x405d7a=inst2
0x4035f7=inst1
0x4035f8=inst2
0x4035f8=inst1
0x4035fb=inst2
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Output:

0x5 5
0x1 1
0x3 3
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-- Ken

perl -E "my $foo = (0x0f-0x0e); say $foo;"
1

perl -E "my $foo = (0x10f-0x0e); say $foo;"
257

perl -E "my $foo = (0x10f-0x01); say $foo;"
270
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Where the remaining conversion is left as an exercise to the author of the ill-formatted, gimmé question which I have downvoted for laziness (of a non-Perlish character) and failure to read the directions on formatting.

This section of the Monastery is known as is "Seekers of Perl Wisdom" ...not "Spare me the need to think or to read documentation, tuts, etc." SMTNTTOTRD,T,E is a very unwieldy and ugly title... and not what this site is about.

In addition to following toolic's fine suggestion about honoring the local markup scheme, you may wish to read On asking for help and How do I post a question effectively?.

That would be the devil of a piece of homework ... it could be a real business requirement.   And, in any case, it ought to be comparatively simple as “an exercise for the reader / student.”

In any case, you merely need to read the file two lines at a time ... of course, die() if there is no second-line available.   Yes, that means two read-statements ... one driving the while loop, and the second one within it.   Then in this case you can simply split() each line on the equal-sign character.   Presumably you “know” that the second half of the first line will be inst1, and of the second line, inst2, but once again I think that you should check, and die() if this is not so.   (Pragmatically speaking, only your program will be in a position to detect errors in its input file, and if there is an error in it, don’t let it go undetected and also don’t let it be blamed on you!   If your program runs to completion, it should be an affirmation that the file appears to be correct.)

The final bit of magic is handled by the hex() function, as documented in perldoc -f hex, which will convert your hex-string into an integer.   Do this for each of the two hex-strings that you now have in your hand, and print out the difference.

There are a lot of excellent contributions here. But I thought I could take a crack at this one

#! /usr/bin/perl

my $inst1 = "";
while(<DATA>) {
    chomp;
    if ( /inst1/ ) {
        my ( $hex, $etc ) = split "=";
        $inst1 = $hex;
    }
    elsif ( /inst2/ ) {
        my ( $hex, $etc ) = split "=";
        my $diff = ($inst1 - hex($hex)) & hex("0x0ffffff");
        printf "Diff = %6x hex, and %d decimal.\n", $diff, $diff;
    }
}


__DATA__
0x405d75=inst1 
0x405d7a=inst2 
0x4035f7=inst1 
0x4035f8=inst2 
0x4035f8=inst1 
0x4035fb=inst2 
0x4035fb=inst1 
0x4035fc=inst2 
0x4035fc=inst1 
0x4035fd=inst2 
0x405d7a=inst1 
0x405d81=inst2
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The output is:

C:\scripts>perl hex-and-decimal.pl
Diff = bfa286 hex, and 12558982 decimal.
Diff = bfca08 hex, and 12569096 decimal.
Diff = bfca05 hex, and 12569093 decimal.
Diff = bfca04 hex, and 12569092 decimal.
Diff = bfca03 hex, and 12569091 decimal.
Diff = bfa27f hex, and 12558975 decimal.
[download]

David.

bash-3.00# vi 2hex
"2hex" 12 lines, 191 characters
#!/usr/bin/perl


$deca=hex("0x175");
$decb=hex("0x1aa");

print "0x175 hex is $deca in decimal\n";
print "0x1aa hex is $decb in decimal\n";


$diff = $decb - $deca;

print "the difference is $diff\n";
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