CODEWITHSUNDEEP
clinuxshellenvironment-variables
user9612976
user9612976

Reputation:

Why does my execve() only works when arguments include /bin/?

execve() only works when /bin/ is a prefix to the first argument

e.g. ./test.out ls finds nothing while ./test.out /bin/ls works

execve(argv[1], args, getenv("PATH"))

Upvotes: 0

Views: 247

Answers (2)

Ian Abbott
Ian Abbott

Reputation: 17403

execve does not search the PATH directories. The first parameter needs to refer to an actual file reachable from the current directory, so needs to contain / characters if the file is not in the current directory.

Linux supports execvpe as a GNU extension which is a cross between the execve and execvp POSIX functions. The p means it will search the PATH for the file as long as it contains no / characters. (If it does contain / characters, it will the same as the non-p version.) The e means that a new environment is passed to the function in the third parameter.

OP's code passes an environment to the execve function that contains only the PATH environment variable from the original environment. If that is the intention, the same effect can be performed in a POSIX compliant manner by stripping the environment before calling execvp. This makes use of the extern char **environ; variable declared by #include <unistd.h>:

char *env_p = getenv("PATH");
char *args[] = {argv[1], argv[2], NULL};

if (environ[0]) {
    environ[0] = env_p;
    environ[1] = NULL;
}

if (execvp(argv[1], args) < 0) {
    perror("execvp");
    exit(EXIT_FAILURE);
}

Upvotes: 0

Barmar
Barmar

Reputation: 780909

execve() doesn't search PATH for the executable. You have to use execvp() for that. The p in the name stands for PATH.

Upvotes: 3

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