Section exec Functions
0 is the list of arguments to pass to the program specified no execvp no yes no yes yes no execve yes no no yes no yes. Relationship of the six exec functions. The process ID does not change across an exec, because a new process is not The next difference concerns the passing of the argument list (l stands for list and v . We can illustrate the relationship among these six functions as shown in. #include int execl (const char *pathname, const char *arg0,. The relationship among these six functions is shown in Figure argument to the exec function, with a null pointer terminating the variable number of arguments.
The base of each is exec executefollowed by one or more letters: In the execl, execlp, execv, and execvp calls, the new process image inherits the current environment variables.
Arguments[ edit ] path The argument specifies the path name of the file to execute as the new process image.
Arguments beginning at arg0 are pointers to arguments to be passed to the new process image. The argv value is an array of pointers to arguments. Usually it is the same value as the path argument.
Some programs may incorrectly rely on this argument providing the location of the executable, but there is no guarantee of this nor is it standardized across platforms. The exec calls named ending with an e alter the environment for the new process image by passing a list of environment settings through the envp argument. This argument is an array of character pointers; each element except for the final element points to a null-terminated string defining an environment variable.
UNIX & GNU/Linux - System calls - Using execve()
Each null-terminated string has the form: The final element of the envp array must be null. When a filename argument is specified If filename contains a slash, it is taken as a pathname.
Otherwise, the executable file is searched for in the directories specified by the PATH environment variable. The PATH variable contains a list of directories, called path prefixes, that are separated by colons. The last path prefix specifies the current directory.
A zero-length prefix also means the current directory. It can be specified as a colon at the beginning of the value, two colons in a row, or a colon at the end of the value.
There are security reasons for never including the current directory in the search path. See Garfinkel et al.
UNIX & GNU/Linux - System calls - Using execve() | dayline.info
The next difference concerns the passing of the argument list l stands for list and v stands for vector. The functions execl, execlp, and execle require each of the command-line arguments to the new program to be specified as separate arguments.
We mark the end of the arguments with a null pointer. For the other three functions execv, execvp, and execvewe have to build an array of pointers to the arguments, and the address of this array is the argument to these three functions. If this null pointer is specified by the constant 0, we must explicitly cast it to a pointer; if we don't, it's interpreted as an integer argument.
c - Why first arg to execve() must be path to executable - Stack Overflow
The final difference is the passing of the environment list to the new program. The two functions whose names end in an e execle and execve allow us to pass a pointer to an array of pointers to the environment strings. The other four functions, however, use the environ variable in the calling process to copy the existing environment for the new program.
Recall our discussion of the environment strings in Section 7.