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env(P) env(P)
NAME
env - set the environment for command invocation
SYNOPSIS
env [-i][name=value]... [utility [argument...]]
DESCRIPTION
The env utility shall obtain the current environment,
modify it according to its arguments, then invoke the
utility named by the utility operand with the modified
environment.
Optional arguments shall be passed to utility.
If no utility operand is specified, the resulting envi-
ronment shall be written to the standard output, with
one name= value pair per line.
OPTIONS
The env utility shall conform to the Base Definitions
volume of IEEE Std 1003.1-2001, Section 12.2, Utility
Syntax Guidelines.
The following options shall be supported:
-i Invoke utility with exactly the environment spec-
ified by the arguments; the inherited environment
shall be ignored completely.
OPERANDS
The following operands shall be supported:
name=value
Arguments of the form name= value shall modify
the execution environment, and shall be placed
into the inherited environment before the utility
is invoked.
utility
The name of the utility to be invoked. If the
utility operand names any of the special built-in
utilities in Special Built-In Utilities , the
results are undefined.
argument
A string to pass as an argument for the invoked
utility.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the
execution of env:
LANG Provide a default value for the internationaliza-
tion 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 cate-
gories.)
LC_ALL If set to a non-empty string value, override the
values of all the other internationalization
variables.
LC_CTYPE
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).
LC_MESSAGES
Determine the locale that should be used to
affect the format and contents of diagnostic mes-
sages written to standard error.
NLSPATH
Determine the location of message catalogs for
the processing of LC_MESSAGES .
PATH Determine the location of the utility, as
described in the Base Definitions volume of
IEEE Std 1003.1-2001, Chapter 8, Environment
Variables. If PATH is specified as a name= value
operand to env, the value given shall be used in
the search for utility.
ASYNCHRONOUS EVENTS
Default.
STDOUT
If no utility operand is specified, each name= value
pair in the resulting environment shall be written in
the form:
"%s=%s\n", <name>, <value>
If the utility operand is specified, the env utility
shall not write to standard output.
STDERR
The standard error shall be used only for diagnostic
messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
If utility is invoked, the exit status of env shall be
the exit status of utility; otherwise, the env utility
shall exit with one of the following values:
0 The env utility completed successfully.
1-125 An error occurred in the env utility.
126 The utility specified by utility was found but
could not be invoked.
127 The utility specified by utility could not be
found.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
The command, env, nice, nohup, time, and xargs 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 simi-
lar 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 dis-
tinction between exit codes 126 and 127 is based on
KornShell practice that uses 127 when all attempts to
exec the utility fail with [ENOENT], and uses 126 when
any attempt to exec the utility fails for any other rea-
son.
Historical implementations of the env utility use the
execvp() or execlp() 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 spe-
cial meaning to the shell. Therefore, shell functions,
special built-ins, and built-ins that are only provided
by the shell are not found.
EXAMPLES
The following command:
env -i PATH=/mybin mygrep xyz myfile
invokes the command mygrep with a new PATH value as the
only entry in its environment. In this case, PATH is
used to locate mygrep, which then must reside in /mybin.
RATIONALE
As with all other utilities that invoke other utilities,
this volume of IEEE Std 1003.1-2001 only specifies what
env 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 env.
The -i option was added to allow the functionality of
the withdrawn - option in a manner compatible with the
Utility Syntax Guidelines.
Some have suggested that env is redundant since the same
effect is achieved by:
name=value ... utility [ argument ... ]
The example is equivalent to env when an environment
variable is being added to the environment of the com-
mand, but not when the environment is being set to the
given value. The env utility also writes out the current
environment if invoked without arguments. There is suf-
ficient functionality beyond what the example provides
to justify inclusion of env.
FUTURE DIRECTIONS
None.
SEE ALSO
Parameters and Variables , 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 Operat-
ing System Interface (POSIX), The Open Group Base Speci-
fications Issue 6, Copyright (C) 2001-2003 by the Insti-
tute 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.open-
group.org/unix/online.html .
POSIX 2003 env(P)
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