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

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
10

NAME

12       env — set the environment for command invocation
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SYNOPSIS

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

18       The env utility shall obtain the current environment, modify it accord‐
19       ing  to its arguments, then invoke the utility named by the utility op‐
20       erand with the modified environment.
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22       Optional arguments shall be passed to utility.
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24       If no utility operand is specified, the resulting environment shall  be
25       written to the standard output, with one name=value pair per line.
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27       If the first argument is '-', the results are unspecified.
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OPTIONS

30       The  env  utility  shall  conform  to  the  Base  Definitions volume of
31       POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines, except  for  the
32       unspecified usage of '-'.
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34       The following options shall be supported:
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36       -i        Invoke  utility with exactly the environment specified by the
37                 arguments; the inherited environment shall  be  ignored  com‐
38                 pletely.
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OPERANDS

41       The following operands shall be supported:
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43       name=value
44                 Arguments  of  the form name=value shall modify the execution
45                 environment, and shall be placed into the inherited  environ‐
46                 ment before the utility is invoked.
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48       utility   The name of the utility to be invoked. If the utility operand
49                 names any of the special built-in utilities in Section  2.14,
50                 Special Built-In Utilities, the results are undefined.
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52       argument  A string to pass as an argument for the invoked utility.
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STDIN

55       Not used.
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INPUT FILES

58       None.
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ENVIRONMENT VARIABLES

61       The following environment variables shall affect the execution of env:
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63       LANG      Provide  a  default  value for the internationalization vari‐
64                 ables that are unset or null. (See the Base Definitions  vol‐
65                 ume  of POSIX.1‐2017, Section 8.2, Internationalization Vari‐
66                 ables for the precedence  of  internationalization  variables
67                 used to determine the values of locale categories.)
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69       LC_ALL    If  set  to  a non-empty string value, override the values of
70                 all the other internationalization variables.
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72       LC_CTYPE  Determine the locale for the interpretation of  sequences  of
73                 bytes of text data as characters (for example, single-byte as
74                 opposed to multi-byte characters in arguments).
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76       LC_MESSAGES
77                 Determine the locale that should be used to affect the format
78                 and  contents  of  diagnostic  messages  written  to standard
79                 error.
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81       NLSPATH   Determine the location of message catalogs for the processing
82                 of LC_MESSAGES.
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84       PATH      Determine  the  location  of the utility, as described in the
85                 Base Definitions volume of POSIX.1‐2017, Chapter 8,  Environ‐
86                 ment Variables.  If PATH is specified as a name=value operand
87                 to env, the value given shall be used in the search for util‐
88                 ity.
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ASYNCHRONOUS EVENTS

91       Default.
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STDOUT

94       If no utility operand is specified, each name=value pair in the result‐
95       ing environment shall be written in the form:
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98           "%s=%s\n", <name>, <value>
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100       If the utility operand is specified, the env utility shall not write to
101       standard output.
102

STDERR

104       The standard error shall be used only for diagnostic messages.
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OUTPUT FILES

107       None.
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EXTENDED DESCRIPTION

110       None.
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EXIT STATUS

113       If  utility is invoked, the exit status of env shall be the exit status
114       of utility; otherwise, the env utility shall exit with one of the  fol‐
115       lowing values:
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117           0   The env utility completed successfully.
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119       1-125   An error occurred in the env utility.
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121         126   The  utility  specified  by  utility was found but could not be
122               invoked.
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124         127   The utility specified by utility could not be found.
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CONSEQUENCES OF ERRORS

127       Default.
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129       The following sections are informative.
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APPLICATION USAGE

132       The command, env, nice, nohup, time,  and  xargs  utilities  have  been
133       specified  to use exit code 127 if an error occurs so that applications
134       can distinguish ``failure to find a utility''  from  ``invoked  utility
135       exited  with an error indication''. The value 127 was chosen because it
136       is not commonly used for other meanings; most utilities use small  val‐
137       ues  for  ``normal  error  conditions'' and the values above 128 can be
138       confused with termination due to receipt of a signal. The value 126 was
139       chosen in a similar manner to indicate that the utility could be found,
140       but not invoked. Some scripts produce meaningful error messages differ‐
141       entiating the 126 and 127 cases. The distinction between exit codes 126
142       and 127 is based on KornShell practice that uses 127 when all  attempts
143       to  exec  the utility fail with [ENOENT], and uses 126 when any attempt
144       to exec the utility fails for any other reason.
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146       Historical implementations of the env utility use the execvp() or  exe‐
147       clp() functions defined in the System Interfaces volume of POSIX.1‐2017
148       to invoke the specified utility; this provides better  performance  and
149       keeps  users  from  having to escape characters with special meaning to
150       the shell. Therefore, shell functions, special built-ins, and built-ins
151       that are only provided by the shell are not found.
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EXAMPLES

154       The following command:
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156
157           env -i PATH=/mybin:"$PATH" $(getconf V7_ENV) mygrep xyz myfile
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159       invokes  the  command mygrep with a new PATH value as the only entry in
160       its environment other than any variables required by the implementation
161       for  conformance. In this case, PATH is used to locate mygrep, which is
162       expected to reside in /mybin.
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RATIONALE

165       As with all other utilities that invoke other utilities, this volume of
166       POSIX.1‐2017 only specifies what env does with standard input, standard
167       output, standard error, input files, and output files. If a utility  is
168       executed,  it is not constrained by the specification of input and out‐
169       put by env.
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171       The -i option was added to allow the functionality  of  the  removed  -
172       option in a manner compatible with the Utility Syntax Guidelines. It is
173       possible to create a non-conforming environment using the -i option, as
174       it  may remove environment variables required by the implementation for
175       conformance. The following will preserve these environment variables as
176       well as preserve the PATH for conforming utilities:
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178
179           IFS='
180           '
181           # The preceding value should be <space><tab><newline>.
182           # Set IFS to its default value.
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184           set -f
185           # disable pathname expansion
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187           \unalias -a
188           # Unset all possible aliases.
189           # Note that unalias is escaped to prevent an alias
190           # being used for unalias.
191           # This step is not strictly necessary, since aliases are not inherited,
192           # and the ENV environment variable is only used by interactive shells,
193           # the only way any aliases can exist in a script is if it defines them
194           # itself.
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196           unset -f env getconf
197           # Ensure env and getconf are not user functions.
198
199           env -i $(getconf V7_ENV) PATH="$(getconf PATH)" command
200
201       Some  have  suggested  that  env  is redundant since the same effect is
202       achieved by:
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204
205           name=value ... utility [ argument ... ]
206
207       The example is equivalent to env when an environment variable is  being
208       added  to  the environment of the command, but not when the environment
209       is being set to the given value.  The env utility also writes  out  the
210       current  environment  if invoked without arguments. There is sufficient
211       functionality beyond what the example provides to justify inclusion  of
212       env.
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FUTURE DIRECTIONS

215       None.
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SEE ALSO

218       Section  2.14,  Special Built-In Utilities, Section 2.5, Parameters and
219       Variables
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221       The Base Definitions volume of  POSIX.1‐2017,  Chapter  8,  Environment
222       Variables, Section 12.2, Utility Syntax Guidelines
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225       Portions  of  this text are reprinted and reproduced in electronic form
226       from IEEE Std 1003.1-2017, Standard for Information Technology --  Por‐
227       table  Operating System Interface (POSIX), The Open Group Base Specifi‐
228       cations Issue 7, 2018 Edition, Copyright (C) 2018 by the  Institute  of
229       Electrical  and  Electronics Engineers, Inc and The Open Group.  In the
230       event of any discrepancy between this version and the original IEEE and
231       The  Open Group Standard, the original IEEE and The Open Group Standard
232       is the referee document. The original Standard can be  obtained  online
233       at http://www.opengroup.org/unix/online.html .
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235       Any  typographical  or  formatting  errors that appear in this page are
236       most likely to have been introduced during the conversion of the source
237       files  to  man page format. To report such errors, see https://www.ker
238       nel.org/doc/man-pages/reporting_bugs.html .
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242IEEE/The Open Group                  2017                              ENV(1P)
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