getopt

PURPOSE

     Parses command line flags and parameters.

SYNOPSIS
     set -- `getopt optstring $*`


DESCRIPTION

     The getopt command is used  to break up flags and parame-
     ters in  command lines for  easy parsing by  shell proce-
     dures and to check for valid flags.  opstring is a string
     of recognized  flags (see  the getopt subroutine  call in
     AIX  Operating  System  Technical  Reference).   Extended
     characters  are  not  permitted.    If  a  letter  within
     opstring is followed by a  colon, the flag is expected to
     take a modifying  parameter that may or may  not be sepa-
     rated from it on the command  line by one or more tabs or
     spaces.  If you specify -- as  the last flag on a command
     line processed by getopt,  getopt recognizes it and stops
     its processing; otherwise, getopt creates the terminating
     --.  In either  case, getopt places it at the  end of the
     flags.

     When the output from getopt  is passed by command substi-
     tution to  the shell set  command, set resets all  of the
     shell positional parameters ($1, $2 .  . . ) so that each
     flag  is preceded  by a  - (minus)  and occupies  its own
     positional parameter.  Each  parameter (for example, file
     names and other  parameters) is also parsed  into its own
     positional parameter.

     The  getopt command  writes a  message to  standard error
     when it encounters a flag  not included in opstring.  The
     set command returns a nonzero  value if a flag appears on
     the command line but is  not specified in opstring.  Con-
     sequently, you can test the  validity of command flags by
     testing the  value of  the shell variable  $?.  If  it is
     nonzero, the command line contains an unrecognized flag.

EXAMPLE

     The following  shell procedure is  a front end to  the ar
     command.  It uses getopt to separate the flags and param-
     eters, then  translates them  into the ar  command syntax
     and runs ar with these flags.

       # @(#) lib: Front end to the ar command.
       #
       # Accepts the following flags:
       #    ar flags with "-" prefixes.  See the ar command.
       #    -L library   The default library is "libsubs.a".
       # Note: "lib -r -b sub1.o -v -l newsub.o" performs
       #       "ar rbvl sub1.o libsubs.a newsub.o".
       #       The ar command DOES interpret this correctly.
       set -- `getopt clsvmrua:b:i:dpqtxwL: $*`
       if [ $? != 0 ]          # Test for syntax error
       then
          exit 2
       fi
       FLAGS=  POSNAME=  LIBRARY=libsubs.a     # Default library name
       while [ $1 != -- ]
       do
          case $1 in
             -L)
                LIBRARY=$2
                shift; shift   # Shift past the -L and library name
                ;;
             -a|-b|-i)
                FLAGS=$FLAGS`expr "$1" : "-\(.\)"`
                POSNAME=$2
                shift; shift   # Shift past the flag and parameter
                ;;
             -*)               # Strip the "-" from the flag
                FLAGS=$FLAGS`expr "$1" : "-\(.\)"`
                shift
                ;;
          esac
       done
       shift                   # Shift past the "--" from getopt
       FLAGS=${FLAGS:-vt}      # Default if action not specified
       ar $FLAGS $POSNAME $LIBRARY $*

     If this shell procedure is  stored in a file named "lib",
     then all of the following commands are equivalent:

       lib -L mylib.a -v -r -b putfld.o getnam.o getfld.o getaddr.o
       lib -Lmylib.a -v -r -bputfld.o getnam.o getfld.o getaddr.o
       lib -Lmylib.a -vrbputfld.o getnam.o getfld.o getaddr.o
       lib -Lmylib.a -v -rbputfld.o -- getnam.o getfld.o getaddr.o

     In each  of these cases,  getopt breaks down  the command
     into:

       -L mylib.a -v -r -b putfld.o -- getnam.o getfld.o getaddr.o

     The  getopt  command  writes   to  its  standard  output.
     Because  this   command  is  enclosed  in   "` `"  (grave
     accents), the shell takes its standard output and uses it
     to construct the command:

       set -- -L mylib.a -v -r -b putfld.o -- getnam.o
       getfld.o getaddr.o

     This is  called command substitution.  For  more details,
     see "Command Substitution."

     The set  command (page  ) sets the  positional parameters
     "$1",  "$2", "$3"  .  . .  to each  of  the values  "-L",
     "mylib.a", "-v"  . . . , respectively.

     The shell  procedure then uses the  positional parameters
     to construct and run the command:

       ar vrb putfld.o mylib.a getnam.o getfld.o getaddr.o

     The ar command (page 67)  accepts the flags in any order.
     Therefore, you can  specify flags to "lib"  in any order,
     as long as a parameter  immediately follows a -a, -b, -i,
     or -L flag, and all the flags come before any file names.
     This means that:

       lib -bputfld.o -rv -Lmylib.a getnam.o getfld.o getaddr.o

     produces the command:

       ar brv putfld.o mylib.a getnam.o getfld.o getaddr.o

     which performs  the same action  as each of  the previous
     commands.  See  "test" and  "expr"  for  more information
     about these commands.

RELATED INFORMATION

     The following command:  "sh."

     The getopt  subroutine in AIX Operating  System Technical
     Reference.