Bash Extended Globbing gives syntax error

Solution 1:

Because extglob doesn't work that way. You must put one of the modifier characters at the beginning of your pattern list ((txt|doc) in this case), as follows (from man bash):

          ?(pattern-list)
                 Matches zero or one occurrence of the given patterns
          *(pattern-list)
                 Matches zero or more occurrences of the given patterns
          +(pattern-list)
                 Matches one or more occurrences of the given patterns
          @(pattern-list)
                 Matches one of the given patterns
          !(pattern-list)
                 Matches anything except one of the given patterns

Specifically, ls *.*(txt|doc) produces the behaviour I am guessing you want.

Solution 2:

You can do this without the extended globbing using brace expansion: ls *.{txt,doc}