unix 下的C开发手册,还用详细的例程。

																				env																The Single UNIX ® Specification, Version 2				Copyright © 1997 The Open Group												 NAME				env - set the environment for command invocation				 SYNOPSIS												env [-i][name=value]... [utility [argument...]]								env [-][name=value]... [utility [argument...]]												 DESCRIPTION				The				env				utility will 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 will be passed to				utility.								If no				utility				operand is specified,				the resulting environment will be written to the standard output, with one				name=value				pair per line.				 OPTIONS				The				env				utility supports the XBD specification, Utility Syntax Guidelines  ,				except for its non-standard usage of "-".								The following options are supported:												-i				-				Invoke				utility				with exactly the environment specified by				the arguments; the inherited environment will be ignored completely.												 OPERANDS				The following operands are supported:												name=value				Arguments of the form				name=value				modify the execution environment,				and are placed into the inherited environment				before the				utility				is invoked.								utilityThe 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 affect the execution of				env:												LANGProvide a default value for the internationalisation variables				that are unset or null.				If				LANG				is unset or null, the corresponding value from the				implementation-dependent default locale will be used.				If any of the internationalisation variables contains an invalid setting, the				utility will behave as if none of the variables had been defined.								LC_ALL				If set to a non-empty string value,				override the values of all the other internationalisation variables.								LC_CTYPE				Determine the				locale for the interpretation of sequences of bytes of text data as				characters (for example, single- 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 catalogues				for the processing of				LC_MESSAGES .								PATHDetermine the location of the				utility,				as described in				the XBD specification, Environment Variables  .				If				PATH				is specified as a				name=value				operand to				env,				the				value				given will 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 will be written in the form:								"%s=%s\n", <name>,				<value>												If the				utility				operand is specified, the				env				utility will not write to standard output.				 STDERR				Used only for diagnostic messages.				 OUTPUT FILES				None.				 EXTENDED DESCRIPTION				None.				 EXIT STATUS				If the				utility				utility is invoked, the exit status of				env				will be the				exit status of				utility;				otherwise, the				env				utility will exit with one of the following values:												0The				env				utility completed successfully.								1-125An error occurred in the				env				utility.								126The utility specified by				utility				was found but could not be invoked.								127The utility specified by				utility				could not be found.												 CONSEQUENCES OF ERRORS				Default.				 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 XSH specification				execvp()				or				execlp()				functions				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.				 FUTURE DIRECTIONS				None.				 SEE ALSO								Parameters and Variables				.												UNIX ® is a registered Trademark of The Open Group.				Copyright © 1997 The Open Group				 [ Main Index | XSH | XCU | XBD | XCURSES | XNS ]