1READ(1P) POSIX Programmer's Manual READ(1P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 read - read a line from standard input
13
15 read [-r] var...
16
18 The read utility shall read a single line from standard input.
19 By default, unless the -r option is specified, backslash ( '\' ) shall
21 act as an escape character, as described in Escape Character (Back‐
22 slash) . If standard input is a terminal device and the invoking shell
23 is interactive, read shall prompt for a continuation line when:
24 * The shell reads an input line ending with a backslash, unless the -r
26 option is specified.
27 * A here-document is not terminated after a <newline> is entered.
29 The line shall be split into fields as in the shell (see Field Split‐
31 ting ); the first field shall be assigned to the first variable var,
32 the second field to the second variable var, and so on. If there are
33 fewer var operands specified than there are fields, the leftover fields
34 and their intervening separators shall be assigned to the last var. If
35 there are fewer fields than vars, the remaining vars shall be set to
36 empty strings.
37 The setting of variables specified by the var operands shall affect the
39 current shell execution environment; see Shell Execution Environment .
40 If it is called in a subshell or separate utility execution environ‐
41 ment, such as one of the following:
42 (read foo)
45 nohup read ...
46 find . -exec read ... \;
47 it shall not affect the shell variables in the caller's environment.
49
51 The read utility shall conform to the Base Definitions volume of
52 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
53 The following option is supported:
55 -r Do not treat a backslash character in any special way. Consider
57 each backslash to be part of the input line.
58
61 The following operand shall be supported:
62 var The name of an existing or nonexisting shell variable.
64
67 The standard input shall be a text file.
68
70 None.
71
73 The following environment variables shall affect the execution of read:
74 IFS Determine the internal field separators used to delimit fields;
76 see Shell Variables .
77 LANG Provide a default value for the internationalization variables
79 that are unset or null. (See the Base Definitions volume of
80 IEEE Std 1003.1-2001, Section 8.2, Internationalization Vari‐
81 ables for the precedence of internationalization variables used
82 to determine the values of locale categories.)
83 LC_ALL If set to a non-empty string value, override the values of all
85 the other internationalization variables.
86 LC_CTYPE
88 Determine the locale for the interpretation of sequences of
89 bytes of text data as characters (for example, single-byte as
90 opposed to multi-byte characters in arguments).
91 LC_MESSAGES
93 Determine the locale that should be used to affect the format
94 and contents of diagnostic messages written to standard error.
95 NLSPATH
97 Determine the location of message catalogs for the processing of
98 LC_MESSAGES .
99 PS2 Provide the prompt string that an interactive shell shall write
101 to standard error when a line ending with a backslash is read
102 and the -r option was not specified, or if a here-document is
103 not terminated after a <newline> is entered.
104
107 Default.
108
110 Not used.
111
113 The standard error shall be used for diagnostic messages and prompts
114 for continued input.
115
117 None.
118
120 None.
121
123 The following exit values shall be returned:
124 0 Successful completion.
126 >0 End-of-file was detected or an error occurred.
128
131 Default.
132 The following sections are informative.
134
136 The -r option is included to enable read to subsume the purpose of the
137 line utility, which is not included in IEEE Std 1003.1-2001.
138 The results are undefined if an end-of-file is detected following a
140 backslash at the end of a line when -r is not specified.
141
143 The following command:
144 while read -r xx yy
147 do
148 printf "%s %s\n" "$yy" "$xx"
149 done < input_file
150 prints a file with the first field of each line moved to the end of the
152 line.
153
155 The read utility historically has been a shell built-in. It was sepa‐
156 rated off into its own utility to take advantage of the richer descrip‐
157 tion of functionality introduced by this volume of
158 IEEE Std 1003.1-2001.
159 Since read affects the current shell execution environment, it is gen‐
161 erally provided as a shell regular built-in. If it is called in a sub‐
162 shell or separate utility execution environment, such as one of the
163 following:
164 (read foo)
167 nohup read ...
168 find . -exec read ... \;
169 it does not affect the shell variables in the environment of the call‐
171 er.
172
174 None.
175
177 Shell Command Language
178
180 Portions of this text are reprinted and reproduced in electronic form
181 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
182 -- Portable Operating System Interface (POSIX), The Open Group Base
183 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
184 Electrical and Electronics Engineers, Inc and The Open Group. In the
185 event of any discrepancy between this version and the original IEEE and
186 The Open Group Standard, the original IEEE and The Open Group Standard
187 is the referee document. The original Standard can be obtained online
188 at http://www.opengroup.org/unix/online.html .
189IEEE/The Open Group 2003 READ(1P)