Manual Page - exec(1p)
Manual Reference Pages - EXEC (P)
NAME
exec - execute commands and open, close, or copy file descriptors
CONTENTS
Synopsis
Description
Options
Operands
Stdin
Input Files
Environment Variables
Asynchronous Events
Stdout
Stderr
Output Files
Extended Description
Exit Status
Consequences Of Errors
Application Usage
Examples
Rationale
Future Directions
See Also
Copyright
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 descriptors remain open when the shell invokes
another utility. Scripts concerned 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 command without creating a new process.
If arguments are specified, they shall be arguments to command.
Redirection affects the current shell execution
environment.
OPTIONS
None.
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:
exec 5<&0
Close file descriptor 3:
exec 3<&-
Cat the file maggie by replacing the current shell with the
cat utility:
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 | EXEC (P) | 2003 |
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