Just figured out that hex-to-decimal can be very, very easy from the command prompt:
Set /a 0x7a
Next step might be to convert it into an error message:
Net helpmsg 122
This can be done in a one-liner:
Set /a e=0x7a & (net helpmsg %e%)
Note the parenthesis – without, the e environment variable does not exist when net… is parsed by the interpreter. With parenthesis, it is treated like a separate line.
If you get an error number like -2147024891, you have to remove the upper 16 bits before you get the real error number:
set /a "-2147024891 & 0xffff"
Note that the quotes are necessary to treat & like a bit-wise and.