Originální popis anglicky:
read - read a line from standard input
Návod, kniha: POSIX Programmer's Manual
read [-r] var...
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.
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.
The following operand shall be supported:
- var
- The name of an existing or nonexisting shell variable.
The standard input shall be a text file.
None.
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.
Default.
Not used.
The standard error shall be used for diagnostic messages and prompts for
continued input.
None.
None.
The following exit values shall be returned:
- 0
- Successful completion.
- >0
- End-of-file was detected or an error occurred.
Default.
The following sections are informative.
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.
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.
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.
None.
Shell Command Language
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
.
