"can somebody help me here and tell me whats the mistake i do, and how to correct it"

Did you run this code before posting it? Without bothering to look any further I see Perl give you several pointers to problems:

D:\>perl derp.pl
Unquoted string "inputfile" may clash with future reserved word at der
+p.pl line 24.
Unquoted string "inputfile" may clash with future reserved word at der
+p.pl line 48.
Global symbol "@agents" requires explicit package name at derp.pl line
+ 4.
Global symbol "$session" requires explicit package name at derp.pl lin
+e 4.
Global symbol "$i" requires explicit package name at derp.pl line 5.
Global symbol "$inputfile" requires explicit package name at derp.pl l
+ine 6.
Global symbol "$inputfile" requires explicit package name at derp.pl l
+ine 7.
Global symbol "$agent" requires explicit package name at derp.pl line 
+9.
Global symbol "$i" requires explicit package name at derp.pl line 9.
Global symbol "$agent" requires explicit package name at derp.pl line 
+11.
Global symbol "@agents" requires explicit package name at derp.pl line
+ 11.
Global symbol "$i" requires explicit package name at derp.pl line 13.
Global symbol "$agent" requires explicit package name at derp.pl line 
+15.
Global symbol "$agent" requires explicit package name at derp.pl line 
+17.
Global symbol "$choice" requires explicit package name at derp.pl line
+ 23.
Global symbol "$fVal" requires explicit package name at derp.pl line 2
+6.
Global symbol "$line" requires explicit package name at derp.pl line 2
+7.
Global symbol "$line" requires explicit package name at derp.pl line 2
+8.
Global symbol "$fVal" requires explicit package name at derp.pl line 3
+0.
Global symbol "$fVal" requires explicit package name at derp.pl line 3
+0.
Global symbol "$choice" requires explicit package name at derp.pl line
+ 30.
Global symbol "$line" requires explicit package name at derp.pl line 3
+2.
Global symbol "$choice" requires explicit package name at derp.pl line
+ 32.
Global symbol "$Agtname" requires explicit package name at derp.pl lin
+e 34.
Global symbol "$line" requires explicit package name at derp.pl line 3
+4.
Global symbol "$Agtname" requires explicit package name at derp.pl lin
+e 35.
Global symbol "$Agtname" requires explicit package name at derp.pl lin
+e 36.
Global symbol "$value" requires explicit package name at derp.pl line 
+37.
Global symbol "$val" requires explicit package name at derp.pl line 38
+.
Execution of derp.pl aborted due to compilation errors.
[download]

Consider fixing these problems first.