open(FILE,$path1/build.log) or die "$!\n"; why this will not open the build.log?

In case it's not just a typo in this post...  you'd need to either interpolate

open(FILE,"$path1/build.log") or die "$!\n";
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or concatenate the strings

open(FILE,$path1."/build.log") or die "$!\n";
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Using strictures would have revealed the problem. With use strict; you'd have gotten:

Bareword "build" not allowed while "strict subs" in use at ./626616.pl
+ line 8.
Execution of ./626616.pl aborted due to compilation errors.
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and with use warnings; even more:

Unquoted string "build" may clash with future reserved word at ./62661
+6.pl line 8.
Name "main::FILE" used only once: possible typo at ./626616.pl line 8.
Argument "build" isn't numeric in division (/) at ./626616.pl line 8.
Argument "." isn't numeric in division (/) at ./626616.pl line 8.
Illegal division by zero at ./626616.pl line 8.
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