env

ENV(1P)                     POSIX Programmer's Manual                    ENV(1P)



PROLOG
       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.

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 environment shall be
       written to the standard output, with one name=value pair per line.

       If the first argument is '-', the results are unspecified.

OPTIONS
       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.

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 Section 2.14,
                 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 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.

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
       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.

EXAMPLES
       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.

RATIONALE
       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.

FUTURE DIRECTIONS
       None.

SEE ALSO
       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

COPYRIGHT
       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)