Manpage of READ
Section: POSIX Programmer's Manual (1P)
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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.
read - read 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, as described
in Escape Character (Backslash) . If standard input is a terminal
device and the
invoking shell is interactive, read shall prompt for a continuation
The shell reads an input line ending with a backslash, unless the
-r option is specified.
A here-document is not terminated after a <newline> is entered.
The line shall be split into fields as in the shell (see Field
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 var operands specified than there are fields,
the leftover fields and their intervening separators shall
be assigned to the last var. If there are fewer fields than
vars, the remaining vars shall be set to empty
The setting of variables specified by the var operands shall
affect the current shell execution environment; see Shell Execution
Environment . If it is called in a subshell or separate utility
environment, such as one of the following:
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 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
The following option is supported:
Do not treat a backslash character in any special way. Consider each
backslash to be part of the input line.
The following operand shall be supported:
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
Determine the internal field separators used to delimit fields; see
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables
the precedence of internationalization variables used to determine
the values of locale categories.)
If set to a non-empty string value, override the values of all the
other internationalization variables.
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
Determine the location of message catalogs for the processing of LC_MESSAGES
Provide the prompt string that an interactive shell shall write to
standard error when a line ending with a backslash is read
and the -r option was not specified, or if a here-document is
not terminated after a <newline> is entered.
The standard error shall be used for diagnostic messages and prompts
for continued input.
The following exit values shall be returned:
End-of-file was detected or an error occurred.
CONSEQUENCES OF ERRORS
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 IEEE Std 1003.1-2001.
The results are undefined if an end-of-file is detected following
a backslash at the end of a line when -r is not
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 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 IEEE Std 1003.1-2001.
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:
nohup read ...
find . -exec read ... \;
it does not affect the shell variables in the environment of the caller.
Shell Command Language
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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
- INPUT FILES
- ENVIRONMENT VARIABLES
- ASYNCHRONOUS EVENTS
- OUTPUT FILES
- EXTENDED DESCRIPTION
- EXIT STATUS
- CONSEQUENCES OF ERRORS
- APPLICATION USAGE
- FUTURE DIRECTIONS
- SEE ALSO
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Time: 19:06:18 GMT, October 18, 2011