unix 下的C开发手册,还用详细的例程。

																				cat																The Single UNIX ® Specification, Version 2				Copyright © 1997 The Open Group												 NAME				cat - concatenate and print files				 SYNOPSIS												cat [-u][file ...]												 DESCRIPTION				The				cat				utility reads files in sequence				and writes their contents to the standard output				in the same sequence.				 OPTIONS				The				cat				utility supports the XBD specification, Utility Syntax Guidelines  .								The following option is supported:												-u				Write bytes from the input file to the standard output				without delay as each is read.												 OPERANDS				The following operand is supported:												fileA pathname of an input file.				If no				file				operands are specified,				the standard input is used.				If a				file				is "-", the				cat				utility will read from the standard input at that point in the sequence.				The				cat				utility will not close and reopen standard input when				it is referenced in this way, but will accept multiple occurrences of				"-" as a				file				operand.												 STDIN				The standard input is used only if no				file				operands are specified, or if a				file				operand is "-".				See the INPUT FILES section.				 INPUT FILES				The input files can be any file type.				 ENVIRONMENT VARIABLES				The following environment variables affect the execution of				cat:												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 .												 ASYNCHRONOUS EVENTS				Default.				 STDOUT				The standard output will contain the sequence of bytes read from				the input files.				Nothing else will be written to the standard output.				 STDERR				Used only for diagnostic messages.				 OUTPUT FILES				None.				 EXTENDED DESCRIPTION				None.				 EXIT STATUS				The following exit values are returned:												0All input files were output successfully.								>0An error occurred.												 CONSEQUENCES OF ERRORS				Default.				 APPLICATION USAGE				The				-u				option has value in				prototyping non-blocking reads from FIFOs.				The intent is to support the following sequence:												mkfifo foo				cat -u foo > /dev/tty13 &				cat -u > foo																It is unspecified whether standard output				is or is not buffered in the				default case.				This is sometimes of interest when standard output is associated				with a terminal, since buffering may delay the output.				The presence of the				-u				option guarantees that unbuffered				I/O				is available.				It is implementation-dependent whether the				cat				utility buffers output if the				-u				option is not specified.				Traditionally, the				-u				option is implemented using the				equivalent of the XSH specification				setvbuf()				function.				 EXAMPLES				The following command:												cat myfile												writes the contents of the file				myfile				to standard output.								The following command:												cat doc1 doc2 > doc.all												concatenates the files				doc1				and				doc2				and writes the result to				doc.all.								Because of the shell language mechanism used to				perform output redirection, a				command such as this:												cat doc doc.end > doc												causes the original data in				doc				to be lost.								The command:												cat start - middle - end > file												when standard input is a terminal, gets two arbitrary pieces of				input from the terminal with a single invocation of				cat.				Note, however, that if standard input is a regular file, this would be				equivalent to the command:												cat start - middle /dev/null end > file												because the entire contents of the file would be consumed by				cat				the first time "-" was used as a				file				operand and an end-of-file				condition would be detected immediately when "-" was referenced				the second time.				 FUTURE DIRECTIONS				None.				 SEE ALSO				more.												UNIX ® is a registered Trademark of The Open Group.				Copyright © 1997 The Open Group				 [ Main Index | XSH | XCU | XBD | XCURSES | XNS ]