EVAL(1P)

💅 EVAL(1P) — the POSIX Programmer's Manual page, but make it cute ✨

okay bestie, real talk: this is the EVAL(1P) page from the POSIX Programmer's Manual. That's the whole header, we're moving on 💖

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🎀 PROLOG 🎀

so like, this manual page is part of the POSIX Programmer's Manual. but heads up: the Linux implementation of this interface may differ — so if you're on Linux, go read the corresponding Linux manual page for the actual tea ☕. or... the interface might just not be implemented on Linux at all. rip 🙈

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🌸 NAME 🌸

eval — construct command by concatenating arguments

like. it builds a whole command out of your lil argument pieces. that's the job. that's the gig. 👑

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✨ SYNOPSIS ✨

eval [argument...]

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💜 DESCRIPTION 💜

okay so the eval utility shall construct a command by concatenating arguments together, separating each one with a <space> character. then — and this is the main character moment — the constructed command shall be read and executed by the shell. 🦋

it's giving "build a command, then immediately run it." no cap.

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🔥 OPTIONS 🔥

None.

literally none. not a single flag. we love a low-maintenance icon 💅

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🍓 OPERANDS 🍓

See the DESCRIPTION. (they're the arguments, bestie, they're the whole point)

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🌈 STDIN 🌈

Not used. it doesn't want your input, it's busy ✋

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🧚 INPUT FILES 🧚

None.

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⭐ ENVIRONMENT VARIABLES ⭐

None. no env vars needed, she's self-sufficient 💖

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💫 ASYNCHRONOUS EVENTS 💫

Default.

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🫶 STDOUT 🫶

Not used. nothing gets printed by eval itself, it just does things.

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💀 STDERR 💀

The standard error shall be used only for diagnostic messages. that's it. only for diagnostics. don't expect small talk.

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🎀 OUTPUT FILES 🎀

None.

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🌸 EXTENDED DESCRIPTION 🌸

None. there is no extended description. this section is just standing there. respectfully. 🙈

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👑 EXIT STATUS 👑

okay this part actually matters, listen up:

• If there are no arguments, or only null arguments, eval shall return a zero exit status 💖
• Otherwise, it shall return the exit status of the command defined by the string of concatenated arguments separated by <space> characters
• or a non-zero exit status if the concatenation could not be parsed as a command and the shell is interactive (and therefore did not abort)

⚠️ note the little "and therefore did not abort" — if the shell is interactive it doesn't just die, it hands you a non-zero status instead. know the difference, bestie, it's important 😭

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🦋 CONSEQUENCES OF ERRORS 🦋

Default.

psst — the following sections are informative. (translation: they're helpful commentary, not requirements ✨)

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💅 APPLICATION USAGE 💅

okay so here's the situation: eval is not required to recognize the "--" end of options delimiter. so in cases where the argument(s) to eval might begin with '-', it is recommended that the first argument is prefixed by a string that will not alter the commands to be executed — such as a <space> character:

eval " $commands"

or:

eval " $(some_command)"

see what she did there? a lil sneaky space at the front, and suddenly your args can't get mistaken for options. iconic behavior. 🎀

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🌟 EXAMPLES 🌟

here's the whole vibe, verbatim:

foo=10 x=foo
y='$'$x
echo $y
$foo
eval y='$'$x
echo $y
10

watch the eval line do its lil magic and turn $y into an actual 10. ate. 🔥

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🧠 RATIONALE 🧠

This standard allows, but does not require, eval to recognize "--".

and yes, that means applications cannot use "--" to protect against options supported as an extension (or errors reported for unsupported options). BUT — and this is the slay part — the nature of the eval utility is such that other means can be used to provide this protection (see APPLICATION USAGE above 💖).

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🔮 FUTURE DIRECTIONS 🔮

None.

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💖 SEE ALSO 💖

• Section 2.14, Special Built-In Utilities

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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, for EVAL(1P). go forth and concatenate responsibly. periodt. 💅✨