[KornShell]: Why getopts doesn't detect disabled switches in this script?

Shell Programming and Scripting
1

Hi,

My environement

OS:           Linux Fedora Core 17 X86_64
KSH version:  sh (AT&T Research) 93u+ 2012-08-01

As I understand inside a Kornshell script, the getopts statement allows to collect information about the switches provided for the script (if any). Besides, it is possible to enable/disable those switches respectively by preceding each switch letter with either - or +.

I just wanted to see this in pratice. Therefore I wrote the following code which unfortunately does not give the expected output.

#!/usr/bin/ksh
while getopts :xy arguments
do
    case $arguments in
        x)
            print "x on"
            ;;
        +x)
            print "x off"
            ;;
        y)
            print "y on"
            ;;
        +y)
            print "y off"
            ;;
        \?)
            print "unknown switch"
            ;;
    esac
done

And here is what I get when I run the above script in my linux terminal (myscript.ksh is the name of my script)

$ ./myscript.ksh -x
x on
$ ./myscript.ksh +x
$ ./myscript.ksh -y
y on
$ ./myscript.ksh +y
$

As you can see whenever a switch is preceded by - (therefore enabled) the script prints the corresponding message but whenever it is preceded by the + (disabled) the scripts doesn't seem to do anything and there is no message printed.

Could you kindly help me understand the problem in my script?

Thanks in advance,

2

Could you point out where in the manual page it shows that getopts treats arguments as switches (+x / -x) and not options (-x)?

3

With 1993 and laters versions of ksh , getopts will handle both + and - if you tell it you want it to do that. Change:

while getopts :xy arguments

to:

while getopts +:xy arguments

or:

while getopts :+xy arguments

The November 16, 1988 version of ksh behaved as if the first character of the option string was always '+'.

2 Likes
4

Dear Don, thank you very much for your help which solved the problem! :b:

In fact I saw the use of getopts for switches in the book "KornShell Programming Tutorial" written by Barry Rosenberg for the first time. The author had used :xy and not :+xy. Therefore, either the example in the book had been written for an older version of KSH or simply a typo.

Anyway, thanks to your remark I learnt a new thing today & now the example works.

Thank you very much for your help. :slight_smile:

Regards,