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.\" Copyright (c) 2024 Emma Tebibyte <emma@tebibyte.media>
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.\" Copyright (c) 2024 DTB <trinity@trinity.moe>
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.\"
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.\" This work is licensed under CC BY-SA 4.0. To see a copy of this license,
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.\" visit <http://creativecommons.org/licenses/by-sa/4.0/>.
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.TH rpn 1
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.SH NAME
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rpn \(en reverse polish notation evaluation
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.SH SYNOPSIS
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rpn
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.RB [numbers...]\ [operators...]
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.SH DESCRIPTION
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Rpn parses and and evaluates reverse polish notation either from the standard
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input or by parsing its arguments. See the STANDARD INPUT section.
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For information on for reverse polish notation syntax, see rpn(7).
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.SH STANDARD INPUT
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If rpn is passed arguments, it interprets them as an expression to be evaluated.
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Otherwise, it reads whitespace-delimited numbers and operations from the
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standard input.
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.SH CAVEATS
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Due to precision constraints and the way floats are represented in accordance
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with the IEEE Standard for Floating Point Arithmetic (IEEE 754), floating-point
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arithmetic has rounding errors. This is somewhat curbed by using the
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second-highest float that can be represented in line with this standard to round
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numbers to before outputting.
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.SH DIAGNOSTICS
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If encountering a syntax error, rpn will exit with the appropriate error code
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as defined by sysexits.h(3) and print an error message.
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.SH RATIONALE
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An infix notation calculation utility, bc(1p), is included in the POSIX
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standard, but it doesn’t accept expressions as arguments; in scripts, any
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predefined, non-interactive input must be piped into the program. A dc(1)
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pre-dates the standardized bc(1p), the latter originally being a preprocessor
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for the former, and was included in UNIX v2 onward. While it implements reverse
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polish notation, it still suffers from being unable to accept an expression as
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an argument.
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.SH AUTHOR
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Written by Emma Tebibyte <emma@tebibyte.media>.
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.SH COPYRIGHT
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Copyright (c) 2024 Emma Tebibyte. License AGPLv3+: GNU AGPL version 3 or later
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<https://gnu.org/licenses/agpl.html>.
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.SH SEE ALSO
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rpn(7), bc(1p), dc(1), IEEE 754
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