I wrote and compiled a C and a C++ program in my Red Hat Linux, and the same thing happened both times. I'll give you the C example. I wrote a really simple program called "trial.c", saved it, etc., then compiled it with "gcc", I think. No object files were left. Then, I said "a.out", expecting the program to run, but it just said that "a.out" was an invalid command, even though when I said "ls" it showed "a.out". Any suggestions? Thanks.

./a.out will run it

gcc trial.c -o trial will produce an executable file called trial which you can run using ./trial

You can put "." in your path and you will no longer need to type ./ before the names of local executables.

Wow. That was .easy. .Thanks, .Neumann.

What do you mean put "." in your path? Thanks

Linux doesn't search your current directoy for executables to run by default, but rather only /bin, etc.. It's some sort of security measure. "." means the current directoy. Add it to the PATH environment variable (see a FAQ if you don't know the details of this) if you don't like this measure.

but "/" doesn't mean execute, how does that work?

'Cause Linus said so! Um, no, that's not it. Dot, '.', this directory, then slash, '/', this file? [Maybe?].

. means the current folder, and to reference a file in a folder you put a slash after the foldername. To access the file foo in the folder bar, you'd do "foo/bar". To get the file thwop in the folder "." you do "./thwop".

I hope that makes it clear.

Do not put . in your PATH. If you really want to, then put it at the end so it is searched last. This can open up all sorts of insecurities (e.g. someone puts a trojaned program in the current dir and you run it). If . is at the beggining of the path, and someone puts a trojaned 'ls' in the dir, you can't even see what is in the dir without running the trojan. Bad Stuff.

Of course you can see what's in the directory: just run /bin/ls.

But that requires more typing! Heresy!

ah, i see.

in the end though, you'd be typing the "./" less, so that would make up for the extra "/bin/".

That means we've been wasting our time all along!

But then you'd be adding extra insecurity.

I tried not to make that look serious.
I suck.

Of course, if it's your own machine, then what are the chances someone has put a trojan ls in one of your directories?

well, you could be an idiot

*looks up, noticing everyone look at him after mops last post*

What?

Someone could root your box and install a trojan ls.

I don't see why typing './' is such a problem, the keys are right next to each other (on QWERTY keyboards anyway, I have no idea where they'd be on something like DVORAK).

I meant you'd be an idiot for the reason Unknown_lamer pointed out. Whatever, I need to quit it with the cookie dough.

unknown_lamer, if they could root your box, why would they bother with a trojan?

For future access? Maybe you won't have been rooted, but they gained user level access, and then installed a trojaned ls in the user's home directory. When you go to see what files are in the dir and you have . first in your PATH, then oops the trojaned ls is not running as root and can do stuff like start another program as root and notify the cracker that they now have root, among other things.

Lots of home linux users can be quite careless as well..