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Linux 2.6 - man page for echo (linux section 1posix)

ECHO(P) 			    POSIX Programmer's Manual				  ECHO(P)

NAME
       echo - write arguments to standard output

SYNOPSIS
       echo [string ...]

DESCRIPTION
       The  echo  utility  writes  its	arguments to standard output, followed by a <newline>. If
       there are no arguments, only the <newline> is written.

OPTIONS
       The echo utility shall not recognize the "--" argument in the manner specified  by  Guide-
       line 10 of the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syn-
       tax Guidelines; "--" shall be recognized as a string operand.

       Implementations shall not support any options.

OPERANDS
       The following operands shall be supported:

       string A string to be written to standard output. If the first operand is -n, or if any of
	      the operands contain a backslash ( '\' ) character, the results are implementation-
	      defined.

       On XSI-conformant systems, if the first operand is -n, it shall be treated  as  a  string,
       not  an	option.  The  following character sequences shall be recognized on XSI-conformant
       systems within any of the arguments:

       \a
	      Write an <alert>.

       \b
	      Write a <backspace>.

       \c
	      Suppress the <newline> that otherwise follows the final argument in the output. All
	      characters following the '\c' in the arguments shall be ignored.

       \f
	      Write a <form-feed>.

       \n
	      Write a <newline>.

       \r
	      Write a <carriage-return>.

       \t
	      Write a <tab>.

       \v
	      Write a <vertical-tab>.

       \\
	      Write a backslash character.

       \0num
	      Write an 8-bit value that is the zero, one, two, or three-digit octal number num.

STDIN
       Not used.

INPUT FILES
       None.

ENVIRONMENT VARIABLES
       The following environment variables shall affect the execution of echo:

       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, Inter-
	      nationalization 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  interna-
	      tionalization 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  argu-
	      ments).

       LC_MESSAGES
	      Determine the locale that should be used to affect the format and contents of diag-
	      nostic messages written to standard error.

       NLSPATH
	      Determine the location of message catalogs for the processing of LC_MESSAGES .

ASYNCHRONOUS EVENTS
       Default.

STDOUT
       The echo utility arguments shall be separated by single <space>s  and  a  <newline>  shall
       follow  the  last  argument.	Output	transformations  shall	occur based on the escape
       sequences in the input. See the OPERANDS section.

STDERR
       The standard error shall be used only for diagnostic messages.

OUTPUT FILES
       None.

EXTENDED DESCRIPTION
       None.

EXIT STATUS
       The following exit values shall be returned:

	0     Successful completion.

       >0     An error occurred.

CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.

APPLICATION USAGE
       It is not possible to use echo portably across all POSIX systems unless both  -n  (as  the
       first argument) and escape sequences are omitted.

       The printf utility can be used portably to emulate any of the traditional behaviors of the
       echo utility as follows (assuming that IFS has its standard value or is unset):

	* The historic System V echo and the requirements on XSI implementations in  this  volume
	  of IEEE Std 1003.1-2001 are equivalent to:

	  printf "%b\n" "$*"

	* The BSD echo is equivalent to:

	  if [ "X$1" = "X-n" ]
	  then
	      shift
	      printf "%s" "$*"
	  else
	      printf "%s\n" "$*"
	  fi

       New applications are encouraged to use printf instead of echo.

EXAMPLES
       None.

RATIONALE
       The  echo utility has not been made obsolescent because of its extremely widespread use in
       historical applications.  Conforming applications that wish to do prompting without  <new-
       line>s  or  that  could	possibly be expecting to echo a -n, should use the printf utility
       derived from the Ninth Edition system.

       As specified, echo writes its arguments in the simplest of ways.  The two  different  his-
       torical versions of echo vary in fatally incompatible ways.

       The  BSD  echo checks the first argument for the string -n which causes it to suppress the
       <newline> that would otherwise follow the final argument in the output.

       The System V echo does not support any options, but allows escape sequences within its op-
       erands, as described for XSI implementations in the OPERANDS section.

       The  echo utility does not support Utility Syntax Guideline 10 because historical applica-
       tions depend on echo to echo all of its arguments, except for the -n  option  in  the  BSD
       version.

FUTURE DIRECTIONS
       None.

SEE ALSO
       printf

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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003					  ECHO(P)


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