READ(1) User Commands READ(1)


NAME


read - read a line from standard input

SYNOPSIS


/usr/bin/read [-r] var...


sh
read name...


csh
set variable= $<


ksh
read [-prsu [n]] [name ? prompt] [name]...


ksh93
read [-Aprs] [-d delim] [-n nsize] [-N nsize] [-t timeout][-u unit] [vname?prompt] [vname... ]


DESCRIPTION


/usr/bin/read
The read utility reads a single line from standard input.


By default, unless the -r option is specified, backslash (\) acts as an
escape character. If standard input is a terminal device and the invoking
shell is interactive, read prompts for a continuation line when:

o The shell reads an input line ending with a backslash, unless
the -r option is specified.

o A here-document is not terminated after a NEWLINE character is
entered.


The line is split into fields as in the shell. The first field is
assigned to the first variable var, the second field to the second
variable var, and so forth. If there are fewer var operands specified
than there are fields, the leftover fields and their intervening
separators is assigned to the last var. If there are fewer fields than
vars, the remaining vars is set to empty strings.


The setting of variables specified by the var operands affects the
current shell execution environment. If it is called in a sub-shell 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 caller's environment.


The standard input must be a text file.

sh
One line is read from the standard input and, using the internal field
separator, IFS (normally space or tab), to delimit word boundaries, the
first word is assigned to the first name, the second word to the second
name, and so on, with leftover words assigned to the last name. Lines
can be continued using \newline. Characters other than NEWLINE can be
quoted by preceding them with a backslash. These backslashes are removed
before words are assigned to names, and no interpretation is done on the
character that follows the backslash. The return code is 0, unless an
end-of-file is encountered.

csh
The notation:

set variable = $<


loads one line of standard input as the value for variable. (See csh(1)).

ksh
The shell input mechanism. One line is read and is broken up into fields
using the characters in IFS as separators. The escape character, (\), is
used to remove any special meaning for the next character and for line
continuation. In raw mode, the -r, the , and the \ character are not
treated specially. The first field is assigned to the first name, the
second field to the second name, and so on, with leftover fields assigned
to the last name. The -p option causes the input line to be taken from
the input pipe of a process spawned by the shell using |&. If the -s
flag is present, the input is saved as a command in the history file. The
flag -u can be used to specify a one digit file descriptor unit n to read
from. The file descriptor can be opened with the exec special command.
The default value of n is 0. If name is omitted, REPLY is used as the
default name. The exit status is 0 unless the input file is not open for
reading or an end-of-file is encountered. An end-of-file with the -p
option causes cleanup for this process so that another can be spawned. If
the first argument contains a ?, the remainder of this word is used as a
prompt on standard error when the shell is interactive. The exit status
is 0 unless an end-of-file is encountered.

ksh93
read reads a line from standard input and breaks it into fields using the
characters in the value of the IFS variable as separators. The escape
character, \, is used to remove any special meaning for the next
character and for line continuation unless the -r option is specified.


If there are more variables than fields, the remaining variables are set
to empty strings. If there are fewer variables than fields, the leftover
fields and their intervening separators are assigned to the last
variable. If no var is specified, the variable REPLY is used.


When var has the binary attribute and -n or -N is specified, the bytes
that are read are stored directly into var.


If you specify ?prompt after the first var, read displays a prompt on
standard error when standard input is a terminal or pipe.

OPTIONS


/usr/bin/read, ksh
The following option is supported by /usr/bin/read and ksh:

-r
Do not treat a backslash character in any special way. Considers
each backslash to be part of the input line.


ksh93
The following options are supported by ksh93:

-A
Unset var, and create an indexed array containing each
field in the line starting at index 0.


-d delim
Read until delimiter delim instead of to the end of line.


-n nsize
Read at most nsize bytes. Binary field size is in bytes.


-N nsize
Read exactly nsize bytes. Binary field size is in bytes.


-p
Read from the current co-process instead of standard input.
An end of file causes read to disconnect the co-process so
that another can be created.


-r
Do not treat \ specially when processing the input line.


-s
Save a copy of the input as an entry in the shell history
file.


-t timeout
Specify a timeout in seconds when reading from a terminal
or pipe.


-u fd
Read from file descriptor number fd instead of standard
input. The default value is 0.


-v
When reading from a terminal, display the value of the
first variable and use it as a default value.


OPERANDS


The following operand is supported:

var
The name of an existing or non-existing shell variable.


EXAMPLES


Example 1: Using the read Command




The following example for /usr/bin/read prints a file with the first
field of each line moved to the end of the line:


example% while read -r xx yy
do
printf "%s %s\n" "$yy" "$xx"
done < input_file


ENVIRONMENT VARIABLES


See environ(5) for descriptions of the following environment variables
that affect the execution of read: LANG, LC_ALL, LC_CTYPE, LC_MESSAGES,
and NLSPATH.

IFS
Determines the internal field separators used to delimit fields.


PS2
Provides the prompt string that an interactive shell writes 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 character is entered.


EXIT STATUS


The following exit values are returned:

0
Successful completion.


>0
End-of-file was detected or an error occurred.


ATTRIBUTES


See attributes(5) for descriptions of the following attributes:

/usr/bin/read, csh, ksh, sh

+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|Standard | See standards(5). |
+--------------------+-------------------+

ksh93

+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Uncommitted |
+--------------------+-----------------+

SEE ALSO


csh(1), ksh(1), ksh93(1), line(1), set(1), sh(1), attributes(5),
environ(5), standards(5)


December 18, 2007 READ(1)