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 from standard input into shell variables

SYNOPSIS

       read [-r] var...

DESCRIPTION

       The read utility shall read a single logical line from standard input into one or more shell variables.

       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.1‐2017,  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.1‐2017, 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.1‐2017.

       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.1‐2017, Chapter 8, Environment Variables, Section 12.2, Utility
       Syntax Guidelines

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                          READ(1POSIX)