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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.
OPTIONS
The env utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2,
Utility Syntax Guidelines.
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 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 IEEE Std 1003.1-2001, 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
IEEE Std 1003.1-2001, 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 IEEE Std 1003.1-2001 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 mygrep xyz myfile
invokes the command mygrep with a new PATH value as the only entry in its environment. In this case, PATH
is used to locate mygrep, which then must reside in /mybin.
RATIONALE
As with all other utilities that invoke other utilities, this volume of IEEE Std 1003.1-2001 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 withdrawn - option in a manner compatible with
the Utility Syntax Guidelines.
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
Parameters and Variables , Special Built-In Utilities
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .