man-pages/man1p/env.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "ENV" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" env 
.SH NAME
env \- set the environment for command invocation
.SH SYNOPSIS
.LP
\fBenv\fP \fB[\fP\fB-i\fP\fB][\fP\fIname\fP\fB=\fP\fIvalue\fP\fB]\fP\fB...\fP
\fB[\fP\fIutility\fP
\fB[\fP\fIargument\fP\fB...\fP\fB]]\fP
.SH DESCRIPTION
.LP
The \fIenv\fP utility shall obtain the current environment, modify
it according to its arguments, then invoke the utility named
by the \fIutility\fP operand with the modified environment.
.LP
Optional arguments shall be passed to \fIutility\fP.
.LP
If no \fIutility\fP operand is specified, the resulting environment
shall be written to the standard output, with one
\fIname\fP= \fIvalue\fP pair per line.
.SH OPTIONS
.LP
The \fIenv\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following options shall be supported:
.TP 7
\fB-i\fP
Invoke \fIutility\fP with exactly the environment specified by the
arguments; the inherited environment shall be ignored
completely.
.sp
.SH OPERANDS
.LP
The following operands shall be supported:
.TP 7
\fIname\fP=\fIvalue\fP
Arguments of the form \fIname\fP= \fIvalue\fP shall modify the execution
environment, and shall be placed into the inherited
environment before the \fIutility\fP is invoked.
.TP 7
\fIutility\fP
The name of the utility to be invoked. If the \fIutility\fP operand
names any of the special built-in utilities in \fISpecial Built-In
Utilities\fP , the results are undefined.
.TP 7
\fIargument\fP
A string to pass as an argument for the invoked utility.
.sp
.SH STDIN
.LP
Not used.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIenv\fP:
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fIPATH\fP
Determine the location of the \fIutility\fP, as described in the Base
Definitions volume of IEEE\ Std\ 1003.1-2001, Chapter 8, Environment
Variables. If \fIPATH\fP is specified as a \fIname\fP= \fIvalue\fP
operand to \fIenv\fP, the \fIvalue\fP given shall be used in the search
for \fIutility\fP.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
If no \fIutility\fP operand is specified, each \fIname\fP= \fIvalue\fP
pair in the resulting environment shall be written in
the form:
.sp
.RS
.nf

\fB"%s=%s\\n", <\fP\fIname\fP\fB>, <\fP\fIvalue\fP\fB>
\fP
.fi
.RE
.LP
If the \fIutility\fP operand is specified, the \fIenv\fP utility shall
not write to standard output.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
If \fIutility\fP is invoked, the exit status of \fIenv\fP shall be
the exit status of \fIutility\fP; otherwise, the
\fIenv\fP utility shall exit with one of the following values:
.TP 7
\ \ \ \ 0
The \fIenv\fP utility completed successfully.
.TP 7
1-125
An error occurred in the \fIenv\fP utility.
.TP 7
\ \ 126
The utility specified by \fIutility\fP was found but could not be
invoked.
.TP 7
\ \ 127
The utility specified by \fIutility\fP could not be found.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The \fIcommand\fP, \fIenv\fP, \fInice\fP, \fInohup\fP, \fItime\fP,
and \fIxargs\fP utilities have been specified to use exit code 127
if an error occurs so that
applications can distinguish "failure to find a utility" from "invoked
utility exited with an error indication". The value 127
was chosen because it is not commonly used for other meanings; most
utilities use small values for "normal error conditions" and
the values above 128 can be confused with termination due to receipt
of a signal. The value 126 was chosen in a similar manner to
indicate that the utility could be found, but not invoked. Some scripts
produce meaningful error messages differentiating the 126
and 127 cases. The distinction between exit codes 126 and 127 is based
on KornShell practice that uses 127 when all attempts to
\fIexec\fP the utility fail with [ENOENT], and uses 126 when any attempt
to \fIexec\fP the utility fails for any other
reason.
.LP
Historical implementations of the \fIenv\fP utility use the \fIexecvp\fP()
or \fIexeclp\fP() functions defined in the System Interfaces volume
of IEEE\ Std\ 1003.1-2001
to invoke the specified utility; this provides better performance
and keeps users from having to escape characters with special
meaning to the shell. Therefore, shell functions, special built-ins,
and built-ins that are only provided by the shell are not
found.
.SH EXAMPLES
.LP
The following command:
.sp
.RS
.nf

\fBenv -i PATH=/mybin mygrep xyz myfile
\fP
.fi
.RE
.LP
invokes the command \fImygrep\fP with a new \fIPATH\fP value as the
only entry in its environment. In this case, \fIPATH\fP
is used to locate \fImygrep\fP, which then must reside in \fB/mybin\fP.
.SH RATIONALE
.LP
As with all other utilities that invoke other utilities, this volume
of IEEE\ Std\ 1003.1-2001 only specifies what
\fIenv\fP does with standard input, standard output, standard error,
input files, and output files. If a utility is executed, it
is not constrained by the specification of input and output by \fIenv\fP.
.LP
The \fB-i\fP option was added to allow the functionality of the withdrawn
\fB-\fP option in a manner compatible with the
Utility Syntax Guidelines.
.LP
Some have suggested that \fIenv\fP is redundant since the same effect
is achieved by:
.sp
.RS
.nf

\fBname=value ... utility\fP \fB[\fP \fBargument ...\fP \fB]\fP
.fi
.RE
.LP
The example is equivalent to \fIenv\fP when an environment variable
is being added to the environment of the command, but not
when the environment is being set to the given value. The \fIenv\fP
utility also writes out the current environment if invoked
without arguments. There is sufficient functionality beyond what the
example provides to justify inclusion of \fIenv\fP.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIParameters and Variables\fP , \fISpecial
Built-In Utilities\fP
.SH 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 .