A shell, typically parse a command, then fork (duplicates itself).<\/p>\n
The duplicated process replaces itself using Execvp by the program described in the command<\/p>\n
The other process wait for the duplicated one to exit using waitpid. When that happens it prints the prompt again, ready for the next one to come. And the whole thing restarts again.<\/p>\n
Not a very hard life.<\/p>\n
Here are the important parts of the manpages of the 3 functions :<\/p>\n
Fork<\/strong><\/p>\n NAME SYNOPSIS pid_t fork(void);<\/p>\n DESCRIPTION The child process and the parent process run in separate memory spaces. RETURN VALUE Execvp<\/strong><\/p>\n EXEC(3) Linux Programmer’s Manual EXEC(3)<\/p>\n NAME SYNOPSIS DESCRIPTION<\/p>\n The execvp() function replaces the current process image with The initial argument for this\u00a0function is the name of a file that is The const char *arg can be thought of as arg0, arg1, …, argn. RETURN VALUE
\nfork – create a child process<\/p>\n
\n#include <unistd.h><\/p>\n
\nfork() creates a new process by duplicating the calling process. The
\nnew process is referred to as the child process. The calling process
\nis referred to as the parent process.<\/p>\n
\nAt the time of fork() both memory spaces have the same content.<\/p>\n
\nOn success, the PID of the child process is returned in the parent, and
\n0 is returned in the child. On failure, -1 is returned in the parent,
\nno child process is created, and errno is set appropriately.<\/p>\n
\nexecvp – execute a file<\/p>\n
\n#include <unistd.h>
\nint execvp(const char *file, char *const argv[]);<\/p>\n
\na new process image.<\/p>\n
\nto be executed.<\/p>\n
\nTogether they describe a list of one or more pointers to null-termi\u2010
\nnated strings that represent the argument list available to the exe\u2010
\ncuted program. The first argument, by convention, should point to the
\nfilename associated with the file being executed. The list of argu\u2010
\nments must be terminated by a null pointer, and, since these are vari\u2010
\nadic functions, this pointer must be cast (char *) NULL.<\/p>\n
\nThe exec() functions return only if an error has occurred. The return
\nvalue is -1, and errno is set to indicate the error.<\/p>\n