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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 |
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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.1‐2017, 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.1‐2017, 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.1‐2017, 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.1‐2017 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.1‐2017 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.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 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 .
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 2017 ENV(1P)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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