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

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

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 fol-
lowing:

(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 international-
ization 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 stan-
dard 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 back-
slash 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 speci-
fied.

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.