READ(1POSIX)

💖 READ(1POSIX) 💖

okay so bestie, welcome to the POSIX Programmer's Manual entry for read. Yes, that read. The one you've been using in your while loops this whole time. She's a legend, she's a built-in, and she's about to get her full moment. 🎀

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🌸 PROLOG 🌸

So this manual page is part of the POSIX Programmer's Manual. Heads up though: the Linux implementation of this interface may differ — so if you're on Linux, go check the corresponding Linux manual page for what Linux actually does. Or the interface might not even be implemented on Linux at all. iykyk 💅

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✨ NAME ✨

read — read from standard input into shell variables. That's it, that's the whole vibe. 🦋

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🎀 SYNOPSIS 🎀

read [-r] var...

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💜 DESCRIPTION 💜

The read utility shall read a single logical line from standard input into one or more shell variables. One line, so many variables, she's versatile. 👑

By default — like, unless you pass the -r option — <backslash> shall act as an escape character. An unescaped <backslash> shall preserve the literal value of the following character, with the exception of a <newline>. If a <newline> follows the <backslash>, read shall interpret this as line continuation. The <backslash> and <newline> shall be removed before splitting the input into fields. All other unescaped <backslash> characters shall be 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 it'll keep asking, like a bestie who will get the whole story. 😭

The terminating <newline> (if any) shall be removed from the input, and the results shall be split into fields as in the shell for the results of parameter expansion (see Section 2.6.5, 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 fields than there are var operands, the remaining vars shall be set to empty strings. If there are fewer vars than fields, the last var shall be set to a value comprising the following elements:

• 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 — and this is the part that gets people every single time — 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 ... \;

then it shall not affect the shell variables in the caller's environment. the variables stay in the subshell, bestie, they do not come home with you 💀

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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.

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 mode, 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 gatekeep, she'll make it if it's not there. 💖

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⭐ STDIN ⭐

The standard input shall be a text file.

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🦋 INPUT FILES 🦋

None. nothing to see here ✨

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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 👑
• 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 "hey keep going" prompt 🎀

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🌸 ASYNCHRONOUS EVENTS 🌸

Default. she's chill like that 💜

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✨ STDOUT ✨

Not used. She's not here to output, she's here to assign. 💅

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🎀 STDERR 🎀

The standard error shall be used for diagnostic messages and prompts for continued input. That's where the PS2 prompt shows up. 🫶

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💜 OUTPUT FILES 💜

None. ⭐

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🦋 EXTENDED DESCRIPTION 🦋

None. short and sweet ✨

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🔥 EXIT STATUS 🔥

The following exit values shall be returned:

• 0 — Successful completion. ate, no crumbs 👑
• >0 — End-of-file was detected or an error occurred. rip 😭

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🌈 CONSEQUENCES OF ERRORS 🌈

Default.

The following sections are informative. (read: optional lore, not law) 💖

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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. So read -r is literally carrying the whole legacy on her back. iconic 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. field shuffling, slay 🎀

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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 page, she earned it ✨

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. say it with me: subshell variables do not escape 💀

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. So don't get any ideas. 🙈

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🎀 FUTURE DIRECTIONS 🎀

None. she's done evolving, she's perfect 💖

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💜 SEE ALSO 💜

• Chapter 2, Shell Command Language
• The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables
• The Base Definitions volume of POSIX.1‐2017, 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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and that's the whole page, bestie 💖✨🎀 brought to you by IEEE/The Open Group, dated 2017, filed under READ(1POSIX) — go read some standard input, you've got this. 🦋👑💅