execv and csh in c++

[stewie]

I am trying to execute the shell command:
csh -f -c ls *.cpp
and I tried the follwong code:

  char *arg[]={"-f","-c ls *.cpp",(char *)NULL};
  execv("/bin/csh",arg);
  perror("execv error");

and also this code:

char *arg[]={"csh","-f","-c ls *.cpp",(char *)NULL};
  execvp(arg[0],arg);
  perror("execvp error");

and none of them worked. both times the program exited without displaying anything.

(the complete code also uses fork() before executing)
what is wrong with the code?

[srinathduraisamy]

Can you try the same with system() call

[stewie]

It's part of homework and I am not allowed to use system()

[voidpointer69]

Hi,

Please read the man execvp() carefully.

The arg list should perhaps be "-f" "-c" "ls ...." and null terminated.

Not sure what csh would make of a single arg "-c ls..." as opposed to two args "-c" (exec the following command) "ls..." (list some things).

My experience with c shell is that it is mainly an exercise in bug-avoidance.

execvp "/bin/ls" "*.cpp" "" should also do the trick.

[stewie]

-c "ls *.cpp" doesn't work as well. cant use execvp "/bin/ls" "*.cpp" ""
(ls was just an example... it's not only for ls)

[Rubberman]

The exec functions terminate the current process and start the new one. If you want perror() to run, you need to first fork() your program.

[stewie]

if exec fails then it returns and perror will run. as I said the actual program uses fork(). this is not the problem. exec runs successfully but does not display anything

[chroot]

Try

char *arg[]={ "/bin/csh","-f","-c","ls *.cpp",NULL };
execv(*arg, arg);
perror("execv error");

Comments:
- C and C++ programs expect the 1st arg to be the command name, thus the "bin/csh" in the args list
- execv passes the arguments as a list, thus "-c" is an arg by itself (when you enter a shell command, the shell does the work of splitting the arguments and then call the program with an arg list)
- "ls *.cpp" is also one arg, as you would provide it to a shell. 'csh' will interpret the argument and expand the "*.cpp".

Make sure you have /bin/csh, and that you have at least one ".cpp" file in your current dir to see something