$ a='00abc'
$ echo ${a#0}
0abc

     The following four varieties of parameter expansion  provide
     for  substring  processing.  In  each case, pattern matching
     notation (see patmat), rather than regular expression  nota-
     tion, will be used to evaluate the patterns. If parameter is
     * or @, then all the positional  parameters,  starting  with
     $1,  are substituted (separated by a field separator charac-
     ter). Enclosing  the  full  parameter  expansion  string  in
     double-quotes will not cause the following four varieties of
     pattern characters to be quoted, whereas quoting  characters
     within the braces will have this effect.

     ${parameter%word}
           Remove Smallest  Suffix  Pattern.  The  word  will  be
           expanded to produce a pattern. The parameter expansion
           then will result in parameter, with the smallest  por-
           tion of the suffix matched by the pattern deleted.

     ${parameter%%word}
           Remove  Largest  Suffix  Pattern.  The  word  will  be
           expanded to produce a pattern. The parameter expansion
           then will result in parameter, with the  largest  por-
           tion of the suffix matched by the pattern deleted.

     ${parameter#word}
           Remove Smallest  Prefix  Pattern.  The  word  will  be
           expanded to produce a pattern. The parameter expansion
           then will result in parameter, with the smallest  por-
           tion of the prefix matched by the pattern deleted.

     ${parameter##word}
           Remove  Largest  Prefix  Pattern.  The  word  will  be
           expanded to produce a pattern. The parameter expansion
           then will result in parameter, with the  largest  por-
           tion of the prefix matched by the pattern deleted.