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getopt - parse command options

set -- ` getopt optstring $ * `

The getopts command supersedes getopt. For more information, see NOTES below.

getopt is used to break up options in command lines for easy parsing by shell procedures and to check for legal options. optstring is a string of recognized option letters; see getopt(3C). If a letter is followed by a colon (:), the option is expected to have an argument which may or may not be separated from it by white space. The special option - is used to delimit the end of the options. If it is used explicitly, getopt recognizes it; otherwise, getopt generates it; in either case, getopt places it at the end of the options. The positional parameters ($1 $2 .\|.\|.\|) of the shell are reset so that each option is preceded by a - and is in its own positional parameter; each option argument is also parsed into its own positional parameter.

Example 1 Processing the arguments for a command

The following code fragment shows how one might process the arguments for a command that can take the options -a or -b, as well as the option -o, which requires an argument:

set -- `getopt abo: $*`
if [ $? != 0 ]
then
 echo $USAGE
 exit 2
fi
for i in $*
do
 case $i in
 -a | -b) FLAG=$i; shift;;
 -o) OARG=$2; shift 2;;
 --) shift; break;;
 esac
done

This code accepts any of the following as equivalent:

cmd -aoarg filename1 filename2
cmd -a -o arg filename1 filename2
cmd -oarg -a filename1 filename2
cmd -a -oarg -- filename1 filename2

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE ATTRIBUTE VALUE

CSI enabled

Intro (1), getoptcvt (1), getopts (1), sh (1), shell_builtins (1), getopt (3C), attributes (7) getopt prints an error message on the standard error when it encounters an option letter not included in optstring. Reset optind to 1 when rescanning the options.

getopt does not support the part of Rule 8 of the command syntax standard (see Intro(1)) that permits groups of option-arguments following an option to be separated by white space and quoted. For example,

cmd -a -b -o "xxx z yy" filename

is not handled correctly. To correct this deficiency, use the getopts command in place of getopt.

If an option that takes an option-argument is followed by a value that is the same as one of the options listed in optstring (referring to the earlier EXAMPLES section, but using the following command line:

cmd -o -a filename

getopt always treats it as an option-argument to -o; it never recognizes -a as an option. For this case, the for loop in the example shifts past the filename argument.