Gfilui

I have a situation with ln and cannot solve this even after I've read about ln in help.

Running the following command:

ln -sf /lib/modules/$kernel_version/extra/mISDN_core.ko /lib/modules/$kernel_version/kernel/drivers/isdn/mISDN/mISDN_core.ko

Provides the following error:

ln: invalid option -- '/'

How can I solve it?

I'd suggest replacing the $kernel_version variable with the actual value.

As described below, using the below command with backtick instead of single quote should solve the problem as well:

$ kernel_version=`uname -r`

As mentioned by @steeldriver the error seems to be due to use of single quote instead of backtick which surround the uname -r command.

hence the following sample command:

$ kernel_version='uname -r'
$ ln -sf /tmp/test/$kernel_version/example /tmp/newname
ln: invalid option -- '/'
Try 'ln --help' for more information.

Will be translated to:

$ ln -sf /tmp/test/uname -r/example /tmp/newname
ln: invalid option -- '/'
Try 'ln --help' for more information.

And as @steeldriver wrote: Presumably the error message is about invalid option '/' because -r is a valid option for the ln command

Note that using backtick would work without errors:

$ kernel_version=`uname -r`
$ ln -sf /tmp/test/$kernel_version/example /tmp/newname
$ 
$ ls -l /tmp/newname 
lrwxrwxrwx 1 user user 35 Feb 21 16:02 /tmp/newname -> /tmp/test/4.4.0-112-generic/example

1. Use the $( ... ) notation instead of the old-style backticks `...` for command substitution. It looks better, and nests better. And is less likely to be mixed up with quotes.



2. 
   

   Quote your variables. With the string uname -r in kernel_version, /lib/modules/$kernel_version/extra/mISDN_core.ko expands to the two words /lib/modules/uname and -r/extra/mISDN_core.ko, when you clearly wanted only one filename.

   
   
   

   Quoted, "/lib/modules/$kernel_version/extra/mISDN_core.ko" would expand to /lib/modules/uname -r/extra/mISDN_core.ko as a single word, and you'd get an error from ln because a file by that name does not exist.

   
   


3. 
   

   Not exactly necessary here if you quoted the variables properly, since your filenames start with a slash, but in general you may want to consider adding the double-dash -- to signal the end of options. With filenames starting with dashes it has to be used so that the application can tell the difference between an option and a filename.

   
   
   

   As the classic example, consider what happens if you run rm * in a directory containing a file called -rf. rm -- * prevents the issue (as would rm ./*).

   
   

Without doing (1) or (2), ln indeed sees the string -r/kernel... as one of the arguments, and as GNU ln reads options from all arguments, not just the first ones, it takes -r as a known option, and then errors on /, since -/ is not an option it knows about.

So, in full, what you should do is:

kernel_version=$(uname -r)
ln -sf -- "/lib/modules/$kernel_version/extra/mISDN_core.ko" 
 "/lib/modules/$kernel_version/kernel/drivers/isdn/mISDN/mISDN_core.ko"