getopt(1)

NAME

getopt — parse command options

SYNOPSIS

getopt optstring args

DESCRIPTION

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 whitespace.

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.

getopt recognizes two hyphens (--) to delimit the end of the options. If absent, getopt places -- at the end of the options.

The most common use of getopt is in the shell's set command (see the example below) where getopt converts the command line to a more easily parsed form. getopt writes the modified command line to the standard output.

EXTERNAL INFLUENCES

Environment Variables

LC_MESSAGES determines the language in which messages are displayed.

If LC_MESSAGES is not specified in the environment or is set to the empty string, the value of LANG is used as a default for each unspecified or empty variable.

If LANG is not specified or is set to the empty string, a default of "C" (see lang(5)) is used instead of LANG. If any internationalization variable contains an invalid setting, getopt behaves as if all internationalization variables are set to "C". See environ(5).

International Code Set Support

Single-byte and multibyte character code sets are supported.

DIAGNOSTICS

getopt prints an error message on the standard error when it encounters an option letter that is not included in optstring.

EXAMPLES

The following code fragment processes the arguments for a command that can take the options a or b, and the option o which requires an argument:

set -- `getopt abo: $*` 

if [ $? -ne 0 ]; then 
    echo $USAGE 
    exit 2 
fi 

while [ $# -gt 0 ]; do 
    case $1 in 
    -a | -b) 
        FLAG=$1 
        shift 
        ;; 
    -o) 
        OARG=$2 
        shift 2 
        ;; 
    --) 
        shift 
        break 
        ;; 
    esac 
done 

This code accepts any of the following as equivalent:

cmd -aoarg file file 
cmd -a -o arg file file 
cmd -oarg -a file file 
cmd -a -oarg -- file file 

WARNINGS

getopt option arguments must not be null strings nor contain embedded blanks.