read man page on Archlinux

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READ(1P)		   POSIX Programmer's Manual		      READ(1P)

       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

       readread a line from standard input

       read [−r] var...

       The read utility shall read a single line from standard input.

       By default, unless the −r option is specified, <backslash> shall act as
       an  escape  character. An unescaped <backslash> shall preserve the lit‐
       eral value of the following character, with the exception  of  a	 <new‐
       line>.	If a <newline> follows the <backslash>, the read utility shall
       interpret this as line  continuation.  The  <backslash>	and  <newline>
       shall  be  removed  before  splitting  the input into fields. All other
       unescaped <backslash> characters shall be removed after	splitting  the
       input into fields.

       If standard input is a terminal device and the invoking shell is inter‐
       active, read shall prompt for a continuation  line  when	 it  reads  an
       input line ending with a <backslash> <newline>, unless the −r option is

       The terminating <newline> (if any) shall be removed from the input  and
       the  results shall be split into fields as in the shell for the results
       of parameter expansion (see Section 2.6.5, Field Splitting); the	 first
       field  shall be assigned to the first variable var, the second field to
       the second variable var, and so on. If  there  are  fewer  fields  than
       there  are  var	operands,  the	remaining  vars	 shall be set to empty
       strings. If there are fewer vars than fields, the last var shall be set
       to a value comprising the following elements:

	*  The field that corresponds to the last var in the normal assignment
	   sequence described above

	*  The delimiter(s) that follow the field corresponding	 to  the  last

	*  The	remaining fields and their delimiters, with trailing IFS white
	   space ignored

       The setting of variables specified by the var operands shall affect the
       current	shell execution environment; see Section 2.12, Shell Execution
       Environment.  If it is called in a subshell or separate utility	execu‐
       tion environment, such as one of the following:

	   (read foo)
	   nohup read ...
	   find . −exec read ... \;

       it shall not affect the shell variables in the caller's environment.

       The  read  utility  shall  conform  to  the  Base Definitions volume of
       POSIX.1‐2008, Section 12.2, Utility Syntax Guidelines.

       The following option is supported:

       −r	 Do not treat a <backslash> character in any special way. Con‐
		 sider each <backslash> to be part of the input line.

       The following operand shall be supported:

       var	 The name of an existing or nonexisting shell variable.

       The standard input shall be a text file.


       The following environment variables shall affect the execution of read:

       IFS	 Determine  the	 internal  field  separators  used  to delimit
		 fields; see Section 2.5.3, Shell Variables.

       LANG	 Provide a default value for  the  internationalization	 vari‐
		 ables	that are unset or null. (See the Base Definitions vol‐
		 ume of POSIX.1‐2008, Section 8.2, Internationalization	 Vari‐
		 ables	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).

		 Determine the locale that should be used to affect the format
		 and contents  of  diagnostic  messages	 written  to  standard

       NLSPATH	 Determine the location of message catalogs for the processing

       PS2	 Provide the prompt string that	 an  interactive  shell	 shall
		 write to standard error when a line ending with a <backslash>
		 <newline> is read and the −r option was not specified.


       Not used.

       The standard error shall be used for diagnostic	messages  and  prompts
       for continued input.



       The following exit values shall be returned:

	0    Successful completion.

       >0    End-of-file was detected or an error occurred.


       The following sections are informative.

       The  −r option is included to enable read to subsume the purpose of the
       line utility, which is not included in POSIX.1‐2008.

       The following command:

	   while read −r xx yy
	       printf "%s %s\n$yy$xx"
	   done < input_file

       prints a file with the first field of each line moved to the end of the

       The  read  utility historically has been a shell built-in. It was sepa‐
       rated off into its own utility to take advantage of the richer descrip‐
       tion of functionality introduced by this volume of POSIX.1‐2008.

       Since  read affects the current shell execution environment, it is gen‐
       erally provided as a shell regular built-in. If it is called in a  sub‐
       shell  or  separate  utility  execution environment, such as one of the

	   (read foo)
	   nohup read ...
	   find . −exec read ... \;

       it does not affect the shell variables in the environment of the	 call‐

       Although	 the  standard input is required to be a text file, and there‐
       fore will always end with a <newline> (unless it is an empty file), the
       processing  of  continuation  lines  when the −r option is not used can
       result in the input not ending with a <newline>.	 This  occurs  if  the
       last  line  of the input file ends with a <backslash> <newline>.	 It is
       for this reason that ``if any'' is used in ``The terminating  <newline>
       (if  any)  shall be removed from the input'' in the description.	 It is
       not a relaxation of the requirement for standard input  to  be  a  text


       Chapter 2, Shell Command Language

       The  Base  Definitions  volume  of POSIX.1‐2008, Chapter 8, Environment
       Variables, Section 12.2, Utility Syntax Guidelines

       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),	The  Open  Group  Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
       cal and Electronics Engineers,  Inc  and	 The  Open  Group.   (This  is
       POSIX.1-2008  with  the	2013  Technical Corrigendum 1 applied.) 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 .

       Any  typographical  or  formatting  errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files  to  man page format. To report such errors, see https://www.ker‐ .

IEEE/The Open Group		     2013			      READ(1P)

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