Lists
       A  list  is a sequence of one or more pipelines separated by one of the
       operators ;, &, &&, or ||, and optionally terminated by one of ;, &, or
       <newline>.
              command1 && command2
              command1 || command2

   Compound Commands
       A compound command is one of the following:
       (list) 
              list  is  executed in a subshell environment
       { list; }
              list  is simply executed in the current shell environment.  list
              must be terminated with a newline or semicolon.
       ((expression))
              The expression is evaluated according  to  the  rules  described
              below  under ARITHMETIC EVALUATION.
       [[ expression ]]
              Return  a  status  of  0 or 1 depending on the evaluation of the
              conditional expression expression. 

       for name [ [ in [ word ... ] ] ; ] do list ; done
       for (( expr1 ; expr2 ; expr3 )) ; do list ; done
       select name [ in word ] ; do list ; done
       case word in [ [(] pattern [ | pattern ] ... ) list ;; ] ... esac
       if list; then list; [ elif list; then list; ] ... [ else list; ] fi
       while list-1; do list-2; done
       until list-1; do list-2; done

   Shell Function Definitions
       name () compound-command [redirection]
       function name [()] compound-command [redirection]

   Command Substitution
              $(command)
       or
              `command`

  Arithmetic Expansion
              $((expression))
       The  evaluation  is performed according to the rules listed below under
       ARITHMETIC EVALUATION.

FUNCTIONS
       ............................................... Functions are executed
       in the context of the current shell;  no  new  process  is  created  to
       interpret  them  (contrast  this with the execution of a shell script).
       When a function is executed, the arguments to the function  become  the
       positional parameters during its execution.  The special parameter # is
       updated to reflect the change. 

       Variables local to the function may be declared with the local  builtin
       command.  Ordinarily, variables and their values are shared between the
       function and its caller.


ARITHMETIC EVALUATION
       id++ id--
              variable post-increment and post-decrement
       ++id --id
              variable pre-increment and pre-decrement
       - +    unary minus and plus
       ! ~    logical and bitwise negation
       **     exponentiation
       * / %  multiplication, division, remainder
       + -    addition, subtraction
       << >>  left and right bitwise shifts
       <= >= < >
              comparison
       == !=  equality and inequality
       &      bitwise AND
       ^      bitwise exclusive OR
       |      bitwise OR
       &&     logical AND
       ||     logical OR
       expr?expr:expr
              conditional operator
       = *= /= %= += -= <<= >>= &= ^= |=
              assignment
       expr1 , expr2
              comma

CONDITIONAL EXPRESSIONS
       Conditional  expressions  are  used  by the [[ compound command and the
       test and [ builtin commands to test file attributes and perform  string
       and  arithmetic comparisons.
       -a file
              True if file exists.
       -b file
              True if file exists and is a block special file.
       -c file
              True if file exists and is a character special file.
       -d file
              True if file exists and is a directory.
       -e file
              True if file exists.
       -f file
              True if file exists and is a regular file.
       -g file
              True if file exists and is set-group-id.
       -h file
              True if file exists and is a symbolic link.
       -k file
              True if file exists and its ``sticky'' bit is set.
       -p file
              True if file exists and is a named pipe (FIFO).
       -r file
              True if file exists and is readable.
       -s file
              True if file exists and has a size greater than zero.
       -t fd  True if file descriptor fd is open and refers to a terminal.
       -u file
              True if file exists and its set-user-id bit is set.
       -w file
              True if file exists and is writable.
       -x file
              True if file exists and is executable.
       -G file
              True if file exists and is owned by the effective group id.
       -L file
              True if file exists and is a symbolic link.
       -N file
              True  if  file  exists  and  has been modified since it was last
              read.
       -O file
              True if file exists and is owned by the effective user id.
       -S file
              True if file exists and is a socket.
       file1 -ef file2
              True if file1 and file2 refer to the same device and inode  num-
              bers.
       file1 -nt file2
              True  if  file1  is  newer (according to modification date) than
              file2, or if file1 exists and file2 does not.
       file1 -ot file2
              True if file1 is older than file2, or if file2 exists and  file1
              does not.
       -o optname
              True  if  the  shell option optname is enabled.  See the list of
              options under the description  of  the  -o  option  to  the  set
              builtin below.
       -v varname
              True  if  the shell variable varname is set (has been assigned a
              value).
       -z string
              True if the length of string is zero.
       string
       -n string
              True if the length of string is non-zero.

       string1 == string2
       string1 = string2
              True if the strings are equal.  = should be used with  the  test
              command for POSIX conformance.

       string1 != string2
              True if the strings are not equal.

       string1 < string2
              True if string1 sorts before string2 lexicographically.

       string1 > string2
              True if string1 sorts after string2 lexicographically.

       arg1 OP arg2
              OP  is one of -eq, -ne, -lt, -le, -gt, or -ge.  These arithmetic
              binary operators return true if arg1 is equal to, not equal  to,
              less  than, less than or equal to, greater than, or greater than
              or equal to arg2, respectively.  Arg1 and arg2 may  be  positive
              or negative integers.