path: root/man1p/read.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "READ" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" read 
.SH NAME
read \- read a line from standard input
.SH SYNOPSIS
.LP
\fBread\fP \fB[\fP\fB-r\fP\fB]\fP \fIvar\fP\fB...\fP
.SH DESCRIPTION
.LP
The \fIread\fP utility shall read a single line from standard input.
.LP
By default, unless the \fB-r\fP option is specified, backslash ( \fB'\\'\fP
) shall act as an escape character, as described
in \fIEscape Character (Backslash)\fP . If standard input is a terminal
device and the
invoking shell is interactive, \fIread\fP shall prompt for a continuation
line when:
.IP " *" 3
The shell reads an input line ending with a backslash, unless the
\fB-r\fP option is specified.
.LP
.IP " *" 3
A here-document is not terminated after a <newline> is entered.
.LP
.LP
The line shall be split into fields as in the shell (see \fIField
Splitting\fP );
the first field shall be assigned to the first variable \fIvar\fP,
the second field to the second variable \fIvar\fP, and so on.
If there are fewer \fIvar\fP operands specified than there are fields,
the leftover fields and their intervening separators shall
be assigned to the last \fIvar\fP. If there are fewer fields than
\fIvar\fPs, the remaining \fIvar\fPs shall be set to empty
strings.
.LP
The setting of variables specified by the \fIvar\fP operands shall
affect the current shell execution environment; see \fIShell Execution
Environment\fP . If it is called in a subshell or separate utility
execution
environment, such as one of the following:
.sp
.RS
.nf

\fB(read foo)
nohup read ...
find . -exec read ... \\;
\fP
.fi
.RE
.LP
it shall not affect the shell variables in the caller's environment.
.SH OPTIONS
.LP
The \fIread\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following option is supported:
.TP 7
\fB-r\fP
Do not treat a backslash character in any special way. Consider each
backslash to be part of the input line.
.sp
.SH OPERANDS
.LP
The following operand shall be supported:
.TP 7
\fIvar\fP
The name of an existing or nonexisting shell variable.
.sp
.SH STDIN
.LP
The standard input shall be a text file.
.SH INPUT FILES
.LP
None.
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIread\fP:
.TP 7
\fIIFS\fP
Determine the internal field separators used to delimit fields; see
\fIShell
Variables\fP .
.TP 7
\fILANG\fP
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.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
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).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.TP 7
\fIPS2\fP
Provide the prompt string that an interactive shell shall write to
standard error when a line ending with a backslash is read
and the \fB-r\fP option was not specified, or if a here-document is
not terminated after a <newline> is entered.
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
Not used.
.SH STDERR
.LP
The standard error shall be used for diagnostic messages and prompts
for continued input.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
Successful completion.
.TP 7
>0
End-of-file was detected or an error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
Default.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The \fB-r\fP option is included to enable \fIread\fP to subsume the
purpose of the \fIline\fP utility, which is not included
in IEEE\ Std\ 1003.1-2001.
.LP
The results are undefined if an end-of-file is detected following
a backslash at the end of a line when \fB-r\fP is not
specified.
.SH EXAMPLES
.LP
The following command:
.sp
.RS
.nf

\fBwhile read -r xx yy
do
    printf "%s %s\\n" "$yy" "$xx"
done <\fP \fIinput_file\fP
.fi
.RE
.LP
prints a file with the first field of each line moved to the end of
the line.
.SH RATIONALE
.LP
The \fIread\fP 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.
.LP
Since \fIread\fP 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:
.sp
.RS
.nf

\fB(read foo)
nohup read ...
find . -exec read ... \\;
\fP
.fi
.RE
.LP
it does not affect the shell variables in the environment of the caller.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIShell Command Language\fP
.SH 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 .