env(1p) — Linux manual page


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

PROLOG         top

       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         top

       env — set the environment for command invocation

SYNOPSIS         top

       env [-i] [name=value]... [utility [argument...]]

DESCRIPTION         top

       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         top

       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         top

       The following operands shall be supported:

                 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

STDIN         top

       Not used.

INPUT FILES         top



       The following environment variables shall affect the execution of

       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).

                 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.



STDOUT         top

       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         top

       The standard error shall be used only for diagnostic messages.

OUTPUT FILES         top




EXIT STATUS         top

       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.



       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

       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         top

       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         top

       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:

           # 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.



SEE ALSO         top

       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         top

       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)