syntax and semantic check

[ravioli]

Does the shell perform a syntax and semantic check before commands are sent to the kernel?

Bradley

 

[PHV]

Syntax check for sure, semantic I'm not sure. I would say grammar check.

Hope This Help, PH.
Want to get great answers to your Tek-Tips questions? Have a look at FAQ219-2884

 

[chipperMDW]

[tt]$ echo )
bash: syntax error near unexpected token `)'[/tt]

That's a syntax error. The shell caught it.


[tt]$ cat --i-stink some-file
cat: unrecognized option `--i-stink'
Try `cat --help' for more information.[/tt]

That might be what you'd call a semantic error. The shell doesn't know what options [tt]cat[/tt] will accept, so it just passes them on. Then, when [tt]cat[/tt] sees those options and doesn't know what to do with them, it issues the error.


Now, the shell doesn't normally "send the commands to the kernel." If you run a command called [tt]cat[/tt], the shell just looks for an executable named "cat" in its PATH variable, then spawns a new process based on that executable.

If it's making a system call, like chdir (like from the [tt]cd[/tt] command, then the commands it uses are shell builtins, which means their code to evaluate arguments and perform their function is a part of the shell.

In that case, a part of the shell does do the semantic check, but only because it "is" the command, in a sense.

 

[ravioli]

I think I am beginning to understand. Thank you Chipper and PHV!

Bradley

 

[chipperMDW]

Slightly on topic...

Go to

http://www.gnu.org/fun/jokes/unix.errors.html

for some funny error messages from the shell.

 

[ravioli]

That's hilarious!

Bradley