execlp

execlp is a member of the exec family of functions defined by the POSIX standard, used to replace the current process image with a new program. The “p” suffix indicates that the function searches for the executable file in the directories listed in the PATH environment variable, while the leading “l” denotes that the arguments are passed as a variable‑length list rather than as an array.

The prototype, declared in \<unistd.h\>, is

int execlp(const char *file, const char *arg0, ..., (char *)NULL);

The first argument, *file*, names the program to execute. If *file* does not contain a slash, execlp searches each directory in PATH for an executable file with that name. The subsequent arguments constitute the argument vector passed to the new program, ending with a null pointer. The first argument (arg0) conventionally contains the filename itself, as the new program expects.

On success, execlp does not return; the original process image is entirely replaced. On failure, it returns –1 and sets errno to indicate the error, such as ENOENT (file not found), EACCES (permission denied), or ENOMEM (insufficient memory). Because the function overlays the current process, any open file descriptors, signal dispositions, and environment variables persist unless explicitly altered before the call.

Related functions include execl, execle, execv, execvp, and execvpe, differing in how they accept arguments and whether they perform PATH search. execlp is commonly used after a fork to run a different program in the child process, enabling the parent to continue execution. Care should be taken to avoid passing untrusted input as arguments, as this can lead to command injection or unintended behavior.