PROLOGThis 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.
NAMEread --- read a line from standard input
read [-r] var...
DESCRIPTIONThe 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. An unescaped <backslash> shall preserve the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, the read utility shall interpret this as line continuation. The <backslash> and <newline> shall be removed before splitting the input into fields. All other unescaped <backslash> characters shall be removed after splitting the input into fields. If standard input is a terminal device and the invoking shell is interactive, read shall prompt for a continuation line when it reads an input line ending with a <backslash> <newline>, unless the -r option is specified. The terminating <newline> (if any) shall be removed from the input and the results shall be split into fields as in the shell for the results of parameter expansion (see Section 2.6.5, 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 fields than there are var operands, the remaining vars shall be set to empty strings. If there are fewer vars than fields, the last var shall be set to a value comprising the following elements:
- The field that corresponds to the last var in the normal assignment sequence described above
- The delimiter(s) that follow the field corresponding to the last var
The remaining fields and their delimiters, with trailing
white space ignored
The setting of variables specified by the
operands shall affect the current shell execution environment; see
Section 2.12, 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 ... \;
OPTIONSThe read utility shall conform to the Base Definitions volume of POSIX.1-2008, 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.
OPERANDSThe following operand shall be supported:
- The name of an existing or nonexisting shell variable.
STDINThe standard input shall be a text file.
ENVIRONMENT VARIABLESThe following environment variables shall affect the execution of read:
- Determine the internal field separators used to delimit fields; see Section 2.5.3, Shell Variables.
- Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2008, Section 8.2, Internationalization Variables for 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 error.
- 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> <newline> is read and the -r option was not specified.
STDERRThe standard error shall be used for diagnostic messages and prompts for continued input.
EXIT STATUSThe following exit values shall be returned:
- Successful completion.
- End-of-file was detected or an error occurred.
CONSEQUENCES OF ERRORSDefault.
The following sections are informative.
APPLICATION USAGEThe -r option is included to enable read to subsume the purpose of the line utility, which is not included in POSIX.1-2008.
EXAMPLESThe following command:
while read -r xx yy do printf "%s %s\n$yy$xx" done < input_file
RATIONALEThe 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 POSIX.1-2008. 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 ... \;
SEE ALSOChapter 2, Shell Command Language The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines
COPYRIGHTPortions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 www.unix.org/online.html .
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