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PROLOG | NAME | 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 |
ENV(1P) POSIX Programmer's Manual ENV(1P)
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.
env — set the environment for command invocation
env [−i] [name=value]... [utility [argument...]]
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 environment shall
be written to the standard output, with one name=value pair per line.
If the first argument is '−', the results are unspecified.
The env utility shall conform to the Base Definitions volume of
POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines, except for the
unspecified usage of '−'.
The following options shall be supported:
−i Invoke utility with exactly the environment specified by
the arguments; the inherited environment shall be ignored
completely.
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
Section 2.14, Special Built-In Utilities, the results are
undefined.
argument A string to pass as an argument for the invoked utility.
Not used.
None.
The following environment variables shall affect the execution of
env:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base Definitions
volume of POSIX.1‐2008, Section 8.2, Internationalization
Variables for the precedence of internationalization
variables used to determine the values of locale
categories.)
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 messages 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 POSIX.1‐2008, 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.
Default.
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.
The standard error shall be used only for diagnostic messages.
None.
None.
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.
Default.
The following sections are informative.
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 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 exec the utility fail
with [ENOENT], and uses 126 when any attempt to exec the utility
fails for any other reason.
Historical implementations of the env utility use the execvp() or
execlp() functions defined in the System Interfaces volume of
POSIX.1‐2008 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.
The following command:
env −i PATH=/mybin:"$PATH" $(getconf V7_ENV) mygrep xyz myfile
invokes the command mygrep with a new PATH value as the only entry in
its environment other than any variables required by the
implementation for conformance. In this case, PATH is used to locate
mygrep, which is expected to reside in /mybin.
As with all other utilities that invoke other utilities, this volume
of POSIX.1‐2008 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 removed −
option in a manner compatible with the Utility Syntax Guidelines. It
is possible to create a non-conforming environment using the −i
option, as it may remove environment variables required by the
implementation for conformance. The following will preserve these
environment variables as well as preserve the PATH for conforming
utilities:
IFS='
'
# The preceding value should be <space><tab><newline>.
# Set IFS to its default value.
set −f
# disable pathname expansion
\unalias −a
# Unset all possible aliases.
# Note that unalias is escaped to prevent an alias
# being used for unalias.
# This step is not strictly necessary, since aliases are not inherited,
# and the ENV environment variable is only used by interactive shells,
# the only way any aliases can exist in a script is if it defines them
# itself.
unset −f env getconf
# Ensure env and getconf are not user functions.
env −i $(getconf V7_ENV) PATH="$(getconf PATH)" command
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 command, 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 sufficient functionality beyond what the example provides to
justify inclusion of env.
None.
Section 2.14, Special Built-In Utilities, Section 2.5, Parameters and
Variables
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment
Variables, Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 ENV(1P)