PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

       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         top

       read — read a line from standard input

SYNOPSIS         top

       read [−r] var...

DESCRIPTION         top

       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         top

       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         top

       The following operand shall be supported:

       var       The name of an existing or nonexisting shell variable.

STDIN         top

       The standard input shall be a text file.

INPUT FILES         top

       None.

ENVIRONMENT VARIABLES         top

       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         top

       Default.

STDOUT         top

       Not used.

STDERR         top

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

OUTPUT FILES         top

       None.

EXTENDED DESCRIPTION         top

       None.

EXIT STATUS         top

       The following exit values shall be returned:

        0    Successful completion.

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

CONSEQUENCES OF ERRORS         top

       Default.

       The following sections are informative.

APPLICATION USAGE         top

       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         top

       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         top

       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         top

       None.

SEE ALSO         top

       Chapter 2, Shell Command Language

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

COPYRIGHT         top

       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 .

       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                 2013                            READ(1P)