EXEC(3) Linux Programmer's Manual EXEC(3)
execl, execlp, execle, execv, execvp, execvpe - execute a file
extern char **environ;
int execl(const char *path, const char *arg, ...
/* (char *) NULL */);
int execlp(const char *file, const char *arg, ...
/* (char *) NULL */);
int execle(const char *path, const char *arg, ...
/*, (char *) NULL, char * const envp */);
int execv(const char *path, 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 exec() family of functions replaces the current process image with
a new process image. The functions described in this manual page are
front-ends for execve(2). (See the manual page for execve(2) for fur-
ther details about the replacement of the current process image.)
The initial argument for these functions is the name of a file that is
to be executed.
The const char *arg and subsequent ellipses in the execl(), execlp(),
and execle() functions can be thought of as arg0, arg1, ..., argn.
Together they describe a list of one or more pointers to null-termi-
nated strings that represent the argument list available to the exe-
cuted program. The first argument, by convention, should point to the
filename associated with the file being executed. The list of argu-
ments must be terminated by a null pointer, and, since these are vari-
adic functions, this pointer must be cast (char *) NULL.
The execv(), execvp(), and execvpe() functions provide 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 execle() and execvpe() functions allow the caller to specify the
environment of the executed program via the argument envp. The envp
argument is an array of pointers to null-terminated strings and must be
terminated by a null pointer. The other functions take the environment
for the new process image from the external variable environ in the
Special semantics for execlp() and execvp()
The execlp(), execvp(), and execvpe() functions duplicate the actions
of the shell in searching for an executable file if the specified file-
name does not contain a slash (/) character. The file is sought in the
colon-separated list of directory pathnames specified in the PATH envi-
ronment variable. If this variable isn't defined, the path list
defaults to the current directory followed by the list of directories
returned by confstr(_CS_PATH). (This confstr(3) call typically returns
the value "/bin:/usr/bin".)
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.)
The exec() functions return only if an error has occurred. The return
value is -1, and errno is set to indicate the error.
All of these functions may fail and set errno for any of the errors
specified for execve(2).
The execvpe() function first appeared in glibc 2.11.
For an explanation of the terms used in this section, see
|Interface | Attribute | Value |
|execl(), execle(), execv() | Thread safety | MT-Safe |
|execlp(), execvp(), execvpe() | Thread safety | MT-Safe env |
The execvpe() function is a GNU extension.
On some other systems, the default path (used when the environment does
not contain the variable PATH) has the current working directory listed
after /bin and /usr/bin, as an anti-Trojan-horse measure. Linux uses
here the traditional "current directory first" default path.
The behavior of execlp() and execvp() when errors occur while attempt-
ing 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.
sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3), envi-
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