Variable Substrings

${VAR#pattern}
If the pattern matches the BEGINNING of the variables value, delete the SHORTEST part that matches and return the rest
${VAR##pattern}
If the pattern matches the BEGINNING of the variables value, delete the LONGEST part that matches and return the rest
${VAR%pattern}
If the pattern matches the END of the variables value, delete the SHORTEST part that matches and return the rest
${VAR%%pattern}
If the pattern matches the END of the variables value, delete the LONGEST part that matches and return the rest

On the keyboard the # is on the left (BEGINNING) and the % is on the right (END)

Example

   $ cd
   $ MYVAR='/export/home/derek/my.unix.file'
   $ echo ${MYVAR##/*/}
      my.unix.file
   $ echo ${MYVAR#/*/}
      home/derek/my.unix.file
   $ echo ${MYVAR}
      /export/home/derek/my.unix.file
   $ echo ${MYVAR%.*}
      /export/home/derek/my.unix
   $ echo ${MYVAR%%.*}
      /export/home/derek/my
   $