Generally, Depending on the type of error, there are variables that are Error Indicators, each of these correspond to errors detected by:

1. The Perl Interpreter.
2. C Library.
3. Operating System.
4. External Programs.

These variables can be accessed many ways (they have more than one form), for example you can use $! or $OS_ERROR or $ERRNO to read the current value of the C error number in numeric context also you can use $! in string context to yield the corresponding system error string..

perlvar has valuable information about these different variables.