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



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

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(1)
