Change existing variable value only user enters non-empty string.

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LEARN ABOUT DEBIAN

plan9-getflags

GETFLAGS(8)						      System Manager's Manual						       GETFLAGS(8)

NAME

       getflags, usage - command-line parsing for shell scripts

SYNOPSIS

       getflags $*

       usage [ progname ]

DESCRIPTION

       Getflags  parses  the options in its command-line arguments according to the environment variable $flagfmt.  This variable should be a list
       of comma-separated options.  Each option can be a single letter, indicating that it does not take arguments, or a letter  followed  by  the
       space-separated	names  of  its	arguments.   Getflags prints an rc(1) script on standard output which initializes the environment variable
       $flagx for every option mentioned in $flagfmt.  If the option is not present on the command-line, the script sets that option's flag  vari-
       able  to  an  empty  list.  Otherwise, the script sets that option's flag variable with a list containing the option's arguments or, if the
       option takes no arguments, with the string 1.  The script also sets the variable $* to the list of arguments following  the  options.   The
       final  line  in the script sets the $status variable, to the empty string on success and to the string usage when there is an error parsing
       the command line.

       Usage prints a usage message to standard error.	It creates the message using $flagfmt, as described above, $args, which should contain the
       string to be printed explaining non-option arguments, and $0, the program name (see rc(1)).  If run under sh(1), which does not set $0, the
       program name must be given explicitly on the command line.

EXAMPLE

       Parse the arguments for leak(1):

	      flagfmt='b,s,f binary,r res,x width'
	      args='name | pid list'
	      if(! ifs=() eval `{getflags $*} || ~ $#* 0){
		   usage
		   exit usage
	      }

SOURCE

       /src/cmd/getflags.c
       /src/cmd/usage.c

SEE ALSO

       arg(3)

																       GETFLAGS(8)

Shell Programming and Scripting