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PROLOG
       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.


NAME
       read — read a line from standard input


SYNOPSIS
       read [−r] var...


DESCRIPTION
       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 literal value  of  the  following  character,  with  the  exception  of  a
       <newline>.   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 interactive, read shall prompt for a
       continuation line when it reads an input line ending with a <backslash> <newline>, unless the  −r  option
       is specified.

       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 var

        *  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 execution 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.


OPTIONS
       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. Consider each <backslash> to be part
                 of the input line.


OPERANDS
       The following operand shall be supported:

       var       The name of an existing or nonexisting shell variable.


STDIN
       The standard input shall be a text file.


INPUT FILES
       None.


ENVIRONMENT VARIABLES
       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 variables that are unset or null. (See the
                 Base Definitions volume of POSIX.1‐2008, 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.

       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.


ASYNCHRONOUS EVENTS
       Default.


STDOUT
       Not used.


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


OUTPUT FILES
       None.


EXTENDED DESCRIPTION
       None.


EXIT STATUS
       The following exit values shall be returned:

        0    Successful completion.

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


CONSEQUENCES OF ERRORS
       Default.

       The following sections are informative.


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


EXAMPLES
       The following command:

           while read −r xx yy
           do
               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 line.


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

       Since read affects the current shell execution environment, it is generally provided as a  shell  regular
       built-in.  If  it  is  called in a subshell or separate utility execution environment, such as one of the
       following:

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

       it does not affect the shell variables in the environment of the caller.

       Although the standard input is required to be a text file, and therefore 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 file.


FUTURE DIRECTIONS
       None.


SEE ALSO
       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 Electrical 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
       http://www.unix.org/online.html .

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