# exec

## NAME



           execl, execlp, execle, execv, execvp, execvpe - execute a file
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#include <unistd.h>**
    
           **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)):
    
           **execvpe**():
               _GNU_SOURCE
    


## DESCRIPTION



           The **exec**() family of functions replaces the current process image
           with a new process image.  The functions described in this manual
           page are layered on top of execve(2).  (See the manual page for
           execve(2) for further 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 functions can be grouped based on the letters following the
           "exec" prefix.
    
       **l - execl(), execlp(), execle()**
           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_.
    
           By contrast with the 'l' functions, the 'v' functions (below)
           specify the command-line arguments of the executed program as a
           vector.
    
       **v - execv(), execvp(), execvpe()**
           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.
    
       **e - execle(), execvpe()**
           The environment of the new process image 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.
    
           All other **exec**() functions (which do not include 'e' in the
           suffix) take the environment for the new process image from the
           external variable _environ_ in the calling process.
    
       **p - execlp(), execvp(), execvpe()**
           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 VERSIONS for further details.
    
           **execvpe**() searches for the program using the value of **PATH** from
           the caller's environment, not from the _envp_ argument.
    
           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.)
    
           All other **exec**() functions (which do not include 'p' in the
           suffix) take as their first argument a (relative or absolute)
           pathname that identifies the program to be executed.
    


## RETURN VALUE



           The **exec**() functions return only if an error has occurred.  The
           return value is -1, and _errno_ is set to indicate the error.
    


## ERRORS



           All of these functions may fail and set _errno_ for any of the
           errors specified for execve(2).
    


## ATTRIBUTES



           For an explanation of the terms used in this section, see
           attributes(7).
           ┌──────────────────────────────────┬───────────────┬─────────────┐
           │ **Interface** │ **Attribute** │ **Value** │
           ├──────────────────────────────────┼───────────────┼─────────────┤
           │ **execl**(), **execle**(), **execv**()       │ Thread safety │ MT-Safe     │
           ├──────────────────────────────────┼───────────────┼─────────────┤
           │ **execlp**(), **execvp**(), **execvpe**()    │ Thread safety │ MT-Safe env │
           └──────────────────────────────────┴───────────────┴─────────────┘
    


## VERSIONS



           The default search path (used when the environment does not
           contain the variable **PATH**) shows some variation across systems.
           It generally includes _/bin_ and _/usr/bin_ (in that order) and may
           also include the current working directory.  On some other
           systems, the current working is included after _/bin_ and _/usr/bin_ ,
           as an anti-Trojan-horse measure.  The glibc implementation long
           followed the traditional default where the current working
           directory is included at the start of the search path.  However,
           some code refactoring during the development of glibc 2.24 caused
           the current working directory to be dropped altogether from the
           default search path.  This accidental behavior change is
           considered mildly beneficial, and won't be reverted.
    
           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.
    


## STANDARDS



           **environ**
           **execl**()
           **execlp**()
           **execle**()
           **execv**()
           **execvp**()
                  POSIX.1-2008.
    
           **execvpe**()
                  GNU.
    


## BUGS



           Before glibc 2.24, **execl**() and **execle**() employed realloc(3)
           internally and were consequently not async-signal-safe, in
           violation of the requirements of POSIX.1.  This was fixed in glibc
           2.24.
    
       **Architecture-specific details**
           On sparc and sparc64, **execv**() is provided as a system call by the
           kernel (with the prototype shown above) for compatibility with
           SunOS.  This function is _not_ employed by the **execv**() wrapper
           function on those architectures.
    


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