Originální popis anglicky:
env - set the environment for command invocation
Návod, kniha: POSIX Programmer's Manual
env
[-i][name=value]...
[utility [argument...]]
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.
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.
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.
Not used.
None.
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.
Default.
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.
The standard error shall be used only for diagnostic messages.
None.
None.
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.
Default.
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
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.
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.
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.
None.
Parameters and Variables ,
Special Built-In Utilities
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
.
