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)

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.1‐2008, 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.

OPERANDS         top

       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         top

       Not used.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       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.

ASYNCHRONOUS EVENTS         top

       Default.

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

       None.

EXTENDED DESCRIPTION         top

       None.

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.

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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.

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.1‐2008 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.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       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

COPYRIGHT         top

       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)