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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, 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 line when:
* 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 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 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 strings.
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
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 IEEE Std 1003.1-2001, 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 Shell Variables .
LANG 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 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 is read and the -r option was not specified, or if a here-document is not
terminated after a <newline> is entered.
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 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 specified.
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
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:
(read foo)
nohup read ...
find . -exec read ... \;
it does not affect the shell variables in the environment of the caller.
FUTURE DIRECTIONS
None.
SEE ALSO
Shell Command Language
COPYRIGHT
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 http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 READ(P)