READ(P) POSIX Programmer's Manual READ(P)PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the corresponding
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NAMEread - read a line from standard input
SYNOPSISread [-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 (Back‐
slash) . 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 Split‐
ting ); 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 environ‐
ment, such as one of the following:
(read foo)
nohup read ...
find . -execread ... \;
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 Vari‐
ables 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 sepa‐
rated off into its own utility to take advantage of the richer descrip‐
tion of functionality introduced by this volume of
IEEE Std 1003.1-2001.
Since read affects the current shell execution environment, it is gen‐
erally provided as a shell regular built-in. If it is called in a sub‐
shell or separate utility execution environment, such as one of the
following:
(read foo)
nohup read ...
find . -execread ... \;
it does not affect the shell variables in the environment of the call‐
er.
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)
