EXEC(P) POSIX Programmer s Manual EXEC(P)
PROLOG This manual page is part of the POSIX Programmer s Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.
NAME exec - execute commands and open, close, or copy file descriptors
SYNOPSIS exec [command [argument ...]]
DESCRIPTION The exec utility shall open, close, and/or copy file descriptors as specified by any redirections as part of the command.
If exec is specified without command or arguments, and any file descriptors with numbers greater than 2 are opened with associated redirection statements, it is unspecified whether those file descrip- tors remain open when the shell invokes another utility. Scripts con- cerned that child shells could misuse open file descriptors can always close them explicitly, as shown in one of the following examples.
If exec is specified with command, it shall replace the shell with com- mand without creating a new process. If arguments are specified, they shall be arguments to command. Redirection affects the current shell execution environment.
OPERANDS See the DESCRIPTION.
STDIN Not used.
INPUT FILES None.
ENVIRONMENT VARIABLES None.
ASYNCHRONOUS EVENTS Default.
STDOUT Not used.
STDERR The standard error shall be used only for diagnostic messages.
OUTPUT FILES None.
EXTENDED DESCRIPTION None.
EXIT STATUS If command is specified, exec shall not return to the shell; rather, the exit status of the process shall be the exit status of the program implementing command, which overlaid the shell. If command is not found, the exit status shall be 127. If command is found, but it is not an executable utility, the exit status shall be 126. If a redirection error occurs (see Consequences of Shell Errors ), the shell shall exit with a value in the range 1-125. Otherwise, exec shall return a zero exit status.
CONSEQUENCES OF ERRORS Default.
The following sections are informative.
APPLICATION USAGE None.
EXAMPLES Open readfile as file descriptor 3 for reading:
exec 3< readfile
Open writefile as file descriptor 4 for writing:
exec 4> writefile
Make file descriptor 5 a copy of file descriptor 0:
Close file descriptor 3:
Cat the file maggie by replacing the current shell with the cat util- ity:
exec cat maggie
RATIONALE Most historical implementations were not conformant in that:
foo=bar exec cmd
did not pass foo to cmd.
FUTURE DIRECTIONS None.
SEE ALSO Special Built-In Utilities
COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 EXEC(P)