You can use adb(1) to convert decimal to hexadecimal and hexadecimal to
decimal as follows:

To convert decimal 127 to hex:

  $ echo '0d127=X' | adb

You should receive the following output:

  7F

To convert hex 7F to decimal:

  $ echo '0x7f=D' | adb

You should receive the following output:

  127

Alternatively, the 'typeset' and 'set' shell builtins can be used to do
base conversions.  See sh-posix(1) or ksh(1).