READ(1P)

🎀 PROLOG 🎀

okay bestie, real talk before anything else: this manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so like, go consult the corresponding Linux manual page for details of Linux behavior), or — and this is the part nobody wants to hear — the interface may not be implemented on Linux at all. 💀

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✨ NAME ✨

read — read from standard input into shell variables 🫶

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🦋 SYNOPSIS 🦋

read [-r] var...

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💅 DESCRIPTION 💅

so the read utility is gonna read a single logical line from standard input and drop it into one or more shell variables. that's the whole job. she's simple, she's iconic, she's employed.

By default — like, unless you pass the -r option — <backslash> acts as an escape character. An unescaped <backslash> preserves the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, read interprets that as line continuation — the <backslash> and <newline> both get removed before the input gets split into fields. All the other unescaped <backslash> characters get removed after splitting the input into fields. timing matters, bestie ⏱️

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. so if you're typing and you end with a backslash, she's gonna look at you like 👁️👄👁️ "and then?"

The terminating <newline> (if any) gets removed from the input, and then the results get split into fields exactly like the shell does for the results of parameter expansion (see Section 2.6.5, Field Splitting). The first field goes to the first variable var, the second field to the second var, and so on. If there are fewer fields than there are var operands, the remaining vars get set to empty strings. If there are fewer vars than fields, the last var gets set to a value made of these three things:

• 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 IFS white space ignored

The setting of variables specified by the var operands shall affect the current shell execution environment — see Section 2.12, Shell Execution Environment. But if it's called in a subshell or a separate utility execution environment, like one of these:

(read foo)
nohup read ...
find . -exec read ... \;

then it shall not affect the shell variables in the caller's environment. sorry babe, what happens in the subshell stays in the subshell 🙈

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🔥 OPTIONS 🔥

The read utility shall conform to the Base Definitions volume of POSIX.1-2017, Section 12.2, Utility Syntax Guidelines. (yes ma'am, we follow the 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. raw. unfiltered. no escape shenanigans. 💅

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🍓 OPERANDS 🍓

The following operand shall be supported:

• var — The name of an existing or nonexisting shell variable. (she doesn't have to exist yet, we're manifesting her 🌈)

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👑 STDIN 👑

The standard input shall be a text file.

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🌸 INPUT FILES 🌸

None. nothing. empty. she takes nothing from files, only vibes.

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🧚 ENVIRONMENT VARIABLES 🧚

The following environment variables shall affect the execution of read:

• IFS — Determine the internal field separators used to delimit fields; see Section 2.5.3, Shell Variables.
• LANG — Provide a default value for the internationalization variables that are unset or null. (See the Base Definitions volume of POSIX.1-2017, 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. she overrides everything, main character energy fr fr
• 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> <newline> is read and the -r option was not specified. that's the "you're still typing??" prompt 🫶

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💜 ASYNCHRONOUS EVENTS 💜

Default.

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⭐ STDOUT ⭐

Not used. she has nothing to say to stdout.

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😭 STDERR 😭

The standard error shall be used for diagnostic messages and prompts for continued input.

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🌈 OUTPUT FILES 🌈

None.

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🎀 EXTENDED DESCRIPTION 🎀

None.

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💖 EXIT STATUS 💖

The following exit values shall be returned:

• 0 — Successful completion. slay 💅
• >0 — End-of-file was detected or an error occurred.

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🦋 CONSEQUENCES OF ERRORS 🦋

Default.

The following sections are informative.

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💅 APPLICATION USAGE 💅

The -r option is included to enable read to subsume the purpose of the line utility, which is not included in POSIX.1-2008. she absorbed her predecessor's whole job. icon behavior. 👑

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✨ EXAMPLES ✨

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. lowkey a party trick, highkey useful 🎉

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🔥 RATIONALE 🔥

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 POSIX.1-2017. she got her own solo debut ✨

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.

Although the standard input is required to be a text file, and therefore will always end with a <newline> (unless it is an empty file), the processing of continuation lines when the -r option is not used can result in the input not ending with a <newline>. This occurs if the last line of the input file ends with a <backslash> <newline>. It is for this reason that "if any" is used in "The terminating <newline> (if any) shall be removed from the input" in the description. It is not a relaxation of the requirement for standard input to be a text file. don't try it. the "if any" is doing heavy lifting and it knows it 😤

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🌸 FUTURE DIRECTIONS 🌸

None.

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🧚 SEE ALSO 🧚

• Chapter 2, Shell Command Language
• The Base Definitions volume of POSIX.1-2017, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

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💜 COPYRIGHT 💜

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

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okay that's the whole page, bestie — and the tea at the very bottom is that this icon dropped back in 2017, courtesy of IEEE/The Open Group, filed under READ(1P) in the POSIX Programmer's Manual. go read something from standard input, you deserve it 💖🦋🎀