getopt.1

   1 .\"
   2 .Dd May 2026
   3 .Dt GETOPT 1
   4 .Os
   5 .Sh NAME
   6 .Nm getopt
   7 .Nd parse command options
   8 .Sh SYNOPSIS
   9 .Nm args=\`getopt Ar optstring $*\`
  10 ; errcode=$?; set \-\- $args
  11 .Sh DESCRIPTION
  12 The
  13 .Nm
  14 utility is used to break up options in command lines for easy parsing by
  15 shell procedures, and to check for legal options.
  16 .Ar Optstring
  17 is a string of recognized option letters (see
  18 .Xr getopt 3 ) ;
  19 if a letter is followed by a colon, the option
  20 is expected to have an argument which may or may not be
  21 separated from it by white space.
  22 The special option
  23 .Ql \-\-
  24 is used to delimit the end of the options.
  25 The
  26 .Nm
  27 utility will place
  28 .Ql \-\-
  29 in the arguments at the end of the options,
  30 or recognize it if used explicitly.
  31 The shell arguments
  32 (\fB$1 $2\fR ...) are reset so that each option is
  33 preceded by a
  34 .Ql \-
  35 and in its own shell argument;
  36 each option argument is also in its own shell argument.
  37 .Sh EXIT STATUS
  38 The
  39 .Nm
  40 utility prints an error message on the standard error output and exits with
  41 status > 0 when it encounters an option letter not included in
  42 .Ar optstring .
  43 .Sh EXAMPLES
  44 The following code fragment shows how one might process the arguments
  45 for a command that can take the options
  46 .Fl a
  47 and
  48 .Fl b ,
  49 and the option
  50 .Fl o ,
  51 which requires an argument.
  52 .Bd -literal -offset indent
  53 args=\`getopt abo: $*\`
  54 # you should not use \`getopt abo: "$@"\` since that would parse
  55 # the arguments differently from what the set command below does.
  56 if [ $? -ne 0 ]; then
  57         echo 'Usage: ...'
  58         exit 2
  59 fi
  60 set \-\- $args
  61 # You cannot use the set command with a backquoted getopt directly,
  62 # since the exit code from getopt would be shadowed by those of set,
  63 # which is zero by definition.
  64 while :; do
  65         case "$1" in
  66         \-a|\-b)
  67                 echo "flag $1 set"; sflags="${1#-}$sflags"
  68                 shift
  69                 ;;
  70         \-o)
  71                 echo "oarg is '$2'"; oarg="$2"
  72                 shift; shift
  73                 ;;
  74         \-\-)
  75                 shift; break
  76                 ;;
  77         esac
  78 done
  79 echo "single-char flags: '$sflags'"
  80 echo "oarg is '$oarg'"
  81 .Ed
  82 .Pp
  83 This code will accept any of the following as equivalent:
  84 .Bd -literal -offset indent
  85 cmd \-aoarg file1 file2
  86 cmd \-a \-o arg file1 file2
  87 cmd \-oarg -a file1 file2
  88 cmd \-a \-oarg \-\- file1 file2
  89 .Ed
  90 .Sh SEE ALSO
  91 .Xr getopts 1 ,
  92 .Xr sh 1 ,
  93 .Xr getopt 3
  94 .Sh HISTORY
  95 Written by
  96 .An Henry Spencer ,
  97 working from a Bell Labs manual page.
  98 Behavior believed identical to the Bell version.
  99 .Sh BUGS
 100 Whatever
 101 .Xr getopt 3
 102 has.
 103 .Pp
 104 Arguments containing white space or embedded shell metacharacters
 105 generally will not survive intact; this looks easy to fix but
 106 is not.
 107 People trying to fix
 108 .Nm
 109 or the example in this manpage should check the history of this file
 110 in
 111 .Fx .
 112 .Pp
 113 The error message for an invalid option is identified as coming
 114 from
 115 .Nm
 116 rather than from the shell procedure containing the invocation
 117 of
 118 .Nm ;
 119 this again is hard to fix.
 120 .Pp
 121 The precise best way to use the
 122 .Nm set
 123 command to set the arguments without disrupting the value(s) of
 124 shell options varies from one shell version to another.
 125 .Pp
 126 Each shellscript has to carry complex code to parse arguments halfway
 127 correctly (like the example presented here).
 128 A better getopt-like tool
 129 would move much of the complexity into the tool and keep the client
 130 shell scripts simpler.