read - read a line from standard input
read [-r] var...
The read utility will read 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 will 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 character is
The line will be split into fields as in the shell; the first field will
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
will be assigned to the last var. If there are fewer fields than vars,
the remaining vars will be set to empty strings.
The setting of variables specified by the var operands will 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:
nohup read ...
find . -exec read ... \;
it will not affect the shell variables in the caller's environment.
The read utility supports the XBD specification, Utility Syntax
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 operands are supported:
var The name of an existing or non-existing shell variable.
The standard input must be a text file.
ENVIRONMENT VARIABLES [Toc] [Back]
The following environment variables affect the execution of read:
IFS Determine the internal field separators used to delimit fields.
PS2 Provide the prompt string that an interactive shell will 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 character is entered.
The following exit values are returned:
0 Successful completion. >0 End-of-file was detected or an error
The read utility has historically been a shell built-in.
The -r option is included to enable read to subsume the purpose of the
line utility, which has been marked LEGACY.
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
printf "%s %s0 "$yy" "$xx"
done < input_file
prints a file with the first field of each line moved to the end of the
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