/usr/share/calc/custhelp/sysinfo is in apcalc-common 2.12.4.4-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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    sysinfo - return a calc #define value
SYNOPSIS
    custom("sysinfo" [, infoname]);
TYPES
    infoname	string or int
    return	int, string or null
DESCRIPTION
    This custom function will return the value certain selected #defile
    values.  The infoname arg must be a string that matches the given
    #define name.  For conveience, the case infoname does not matter,
    so "baseb" and "BASEB" refer to the same #define value.
    The return value is either an integer or a string depending on
    the type of #define selected.  If infoname is unknown, NULL is returned.
    If no infoname is given then a list of infonames and meanings
    are printed.  In this case, null is returned.
    If infoname is a number, then it is interpreted as follows:
	0	print all infonames and meanings	(same as no infoname)
	1	print all infonames and values
	2	print all infoname meanings and values
EXAMPLE
    > custom("sysinfo", "baseb")
	    32
    > custom("sysinfo")
    ... a list of infonames and meanings are printed ...
    > custom("sysinfo", 0)
    ... a list of infonames and meanings are printed ...
    > custom("sysinfo", 1)
    ... a list of infonames and values are printed ...
    > custom("sysinfo", 2)
    ... a list of infoname meanings and values are printed ...
LIMITS
    calc must be built with ALLOW_CUSTOM= -DCUSTOM
    calc must be executed with a -C arg.
LIBRARY
    none
SEE ALSO
    custom
## Copyright (C) 1999  Landon Curt Noll
##
## Calc is open software; you can redistribute it and/or modify it under
## the terms of the version 2.1 of the GNU Lesser General Public License
## as published by the Free Software Foundation.
##
## Calc is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
## or FITNESS FOR A PARTICULAR PURPOSE.	 See the GNU Lesser General
## Public License for more details.
##
## A copy of version 2.1 of the GNU Lesser General Public License is
## distributed with calc under the filename COPYING-LGPL.  You should have
## received a copy with calc; if not, write to Free Software Foundation, Inc.
## 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
##
## @(#) $Revision: 30.1 $
## @(#) $Id: sysinfo,v 30.1 2007/03/16 11:10:04 chongo Exp $
## @(#) $Source: /usr/local/src/cmd/calc/custom/RCS/sysinfo,v $
##
## Under source code control:	1997/03/09 23:14:40
## File existed as early as:	1997
##
## chongo <was here> /\oo/\	http://www.isthe.com/chongo/
## Share and enjoy!  :-)	http://www.isthe.com/chongo/tech/comp/calc/
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