#include <unistd.h> extern char **environ; int execl(const char *pathname, const char *arg, ... /* (char *) NULL */); int execlp(const char *file, const char *arg, ... /* (char *) NULL */); int execle(const char *pathname, const char *arg, ... /*, (char *) NULL, char * const envp */); int execv(const char *pathname, char *const argv); int execvp(const char *file, char *const argv); int execvpe(const char *file, char *const argv, char *const envp);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
The initial argument for these functions is the name of a file that is to be executed.
The const char *arg and subsequent ellipses can be thought of as arg0, arg1, ..., argn. Together they describe a list of one or more pointers to null-terminated strings that represent the argument list available to the executed program. The first argument, by convention, should point to the filename associated with the file being executed. The list of arguments must be terminated by a null pointer, and, since these are variadic functions, this pointer must be cast (char *) NULL.
The char *const argv argument is an array of pointers to null-terminated strings that represent the argument list available to the new program. The first argument, by convention, should point to the filename associated with the file being executed. The array of pointers must be terminated by a null pointer.
The environment of the caller is specified via the argument envp. The envp argument is an array of pointers to null-terminated strings and must be terminated by a null pointer.
These functions duplicate the actions of the shell in searching for an executable file if the specified filename does not contain a slash (/) character. The file is sought in the colon-separated list of directory pathnames specified in the PATH environment variable. If this variable isn't defined, the path list defaults to a list that includes the directories returned by confstr(_CS_PATH) (which typically returns the value "/bin:/usr/bin") and possibly also the current working directory; see NOTES for further details.
If the specified filename includes a slash character, then PATH is ignored, and the file at the specified pathname is executed.
In addition, certain errors are treated specially.
If permission is denied for a file (the attempted execve(2) failed with the error EACCES), these functions will continue searching the rest of the search path. If no other file is found, however, they will return with errno set to EACCES.
If the header of a file isn't recognized (the attempted execve(2) failed with the error ENOEXEC), these functions will execute the shell (/bin/sh) with the path of the file as its first argument. (If this attempt fails, no further searching is done.)
|execl(), execle(), execv()||Thread safety||MT-Safe|
|execlp(), execvp(), execvpe()||Thread safety||MT-Safe env|
The behavior of execlp() and execvp() when errors occur while attempting to execute the file is historic practice, but has not traditionally been documented and is not specified by the POSIX standard. BSD (and possibly other systems) do an automatic sleep and retry if ETXTBSY is encountered. Linux treats it as a hard error and returns immediately.
Traditionally, the functions execlp() and execvp() ignored all errors except for the ones described above and ENOMEM and E2BIG, upon which they returned. They now return if any error other than the ones described above occurs.