[ILUG] what does this shell script mean

[Dave Neary]

hrishy samant wrote:
> 
> hey thanks buddy can you also if possible tell me what
> is getopts all about.

"man getopts" tells you that it's a bash builtin (there may also a
getopts in section 3, which does something similar for C programs).

"man bash" followed by a search for getopts yields the passage below
(sorry for the long c&p): 

There's an Advanced-Bash-Scripting-HOWTO which explains in practical
terms how to use this.

Basically 'while getopts "a:bc:" curr_option; do ... done' is the
general form. The colons mean that a and c expect arguments - this pops
one arg at a time off the argument stack and stores it in curr_option,
and for options expecting an argument, the option is put in $OPTARG. If
you preceed the options with a :, then a - is obligatory before the
arguments.

If this isn't enough information for you, God help you ;-)

Cheers,
Dave.

   getopts optstring name [args]
              getopts  is used by shell procedures to parse posi­
              tional parameters.  optstring contains  the  option
              characters to be recognized; if a character is fol­
              lowed by a colon, the option is expected to have an
              argument,  which  should  be  separated  from it by
              white space.  The colon and question  mark  charac­
              ters  may  not  be used as option characters.  Each
              time it is invoked, getopts places the next  option
              in the shell variable name, initializing name if it
              does not exist, and the index of the next  argument
              to  be  processed into the variable OPTIND.  OPTIND
              is initialized to 1 each time the shell or a  shell
              script  is  invoked.   When  an  option requires an
              argument, getopts places  that  argument  into  the
              variable  OPTARG.   The shell does not reset OPTIND
              automatically; it must be  manually  reset  between
              multiple  calls  to  getopts  within the same shell
              invocation if a new set  of  parameters  is  to  be
              used.

              When  the  end  of  options is encountered, getopts
              exits  with  a  return  value  greater  than  zero.
              OPTIND  is set to the index of the first non-option
              argument, and name is set to ?.

              getopts normally parses the positional  parameters,
              but  if  more  arguments are given in args, getopts
              parses those instead.

              getopts can report errors  in  two  ways.   If  the
              first  character  of  optstring  is a colon, silent
              error reporting is used.  In normal operation diag­
              nostic messages are printed when invalid options or
              missing option arguments are encountered.   If  the
              variable OPTERR is set to 0, no error messages will
              be displayed, even if the first character  of  opt­
              string is not a colon.

              If an invalid option is seen, getopts places ? into
              name and, if not silent, prints  an  error  message
              and  unsets  OPTARG.   If  getopts  is  silent, the
              option character found is placed in OPTARG  and  no
              diagnostic message is printed.

              If a required argument is not found, and getopts is
              not silent, a question mark (?) is placed in  name,
              OPTARG  is  unset,  and  a  diagnostic  message  is
              printed.  If getopts is silent, then a colon (:) is
              placed  in  name  and  OPTARG  is set to the option
              character found.

              getopts returns true if  an  option,  specified  or
              unspecified, is found.  It returns false if the end
              of options is encountered or an error occurs.

-- 
David Neary,               E-Mail dave.neary at palamon.ie
Palamon Technologies Ltd.  Phone +353-1-634-5059