Collection of my simple miniature tools, some written to solve a practical problem, some just out of curiosity. They were all developed and used on Linux systems a long time ago. The markdown files I added only recently.
- eol - convert end-of-line styles (Unix, DOS, Mac)
- errno - describe errno values (wraps
strerror) - float - make and dissect IEEE double precision numbers
- ipinfo - show information about an IPv4 address
- isbnck - verify the ISBN check sum
- legick - check/compute a Swiss student "Leginummer"
- mklock - create exclusive lock file (for use in scripts)
- mkpwd - generate random initial passwords (use in scripts)
- signo - describe signal numbers (wraps
strsignal) - uxtime - convert Unix time to human readable local time
- xorit - xor standard input against a string
All tools exit with status 0 if successful, 111 if a temporary error occurred, and 127 if a permanent error occurred, unless stated otherwise in the tool's manual page. All tools come with a manual page.
Technical notes are in the NOTES.md file.
The eol tool converts between the three most common newline
(or end-of-line) conventions: CR+LF (DOS), LF (Unix), CR (Macintosh).
The logical operation “newline” involved two physical motions
in the old teletype machines: return the carriage to the left
margin, and move down to the next line. This found its way into
the ASCII code, which provides those two operations: CR (ASCII 13)
for Carriage Return and LF (ASCII 10) for Line Feed. Apparently,
the Unix community chose just LF and the early Mac designers
decided for CR. By the way, in C, \r is CR and \n is LF.
The International Standard Book Number (ISBN) was devised in the 1960ies and standardised in 1972. Its purpose is to uniquely identify a book and thus facilitate the logistics of publishers and book sellers. ISBNs must be purchased. Its use is optional. The original ISBN was a 9 digit number, followed by a check digit for error detection. When in the early 2000s it became difficult for new publishers to acquire number blocks, the new ISBN-13 system was designed, which is compatible with the European Article Number (EAN). The isbnck tool knows both ISBN-10 and ISBN-13.
The mklock tool provides a simple mechanism for mutual
exclusion in scripts: atomically test if a file exists and
create it if not; if it does exist, signal an error. If this
“test-and-set” operation succeeded, you're alone. When done,
remove the lock file, either explicitly or as the result of
a trap "rm -f my.lock" 0. For example:
mklock /var/run/foo.lock
echo "Doing something alone..."
rm -f /var/run/foo.lockAn IP (Internet Protocol) version 4 address is a 32-bit number. For routing purposes, the first n bits are taken to signify the network, and the remaining 32-n bits are the host within that network. The least address within a network identifies the network itself, and the largest address within a network serves as the broadcast address (send to all hosts in the network). The number n is given either implicitly (derived from the first few bits of the IP address; this is known as class-based routing), or explicily by augmenting the IP address with a netmask or a "slash value". IP addresses are usually written in "dotted decimal notation" like 192.168.15.3; if a "slash value" is provided, it looks like 192.168.15.3/24 (which means that 192.168.15.0 is the network and 3 is the host within this network). The ipinfo tool shows all these values; for example, given 192.168.25.108/27, the tool reports:
CIDR 27 host address, private
Address: 192.168.25.108 11000000.10101000.00011001.011/01100
Netmask: 255.255.255.224 11111111.11111111.11111111.111/00000 27
Hostmask: 0.0.0.31 00000000.00000000.00000000.000/11111 5
MaxHosts: 30 --------+--------+--------+---/-----
Network: 192.168.25.96 11000000.10101000.00011001.011/00000 min
Broadcast: 192.168.25.127 11000000.10101000.00011001.011/11111 max
The manual page for ipinfo may contain additional information. Also see RFC 1519 about CIDR and RFC 1918 about private internet addresses. For information about an IP address's ownership, try whois or one of the online services, e.g. whois.arin.net. Nowadays, IPv6 is widely deployed. An IPv6 address is 128 bits.
Unix maintains (at least) calendar time and CPU time. The uxtime utility shows calendar time, not CPU time.
Calendar time is the number of seconds since the Epoch,
which is 00:00:00 on January 1, 1970, Universal Time
Coordinated (UTC, formely Greenwich Mean Time, GMT).
It is returned by the function time() and stored
in variables of type time_t.
CPU time is measured in clock ticks, which occur at the
constant but system-dependent frequency CLOCKS_PER_SEC.
There is no epoch, only differences of clock values
are meaningful. Clock values are returned by clock()
and have type clock_t.
All functions, types, and definitions above are part
of the <time.h> ANSI C standard header. Note that
clock ticks may overflow clock_t and thus are not
suitable for reliable timings. System functions may
be used, at the price of less portability.
An IEEE 754 binary64 (double precision) floating-point
number is represented as a sign bit S (1 for negative),
an integer exponent E (11 bits), and mantissa M (52 bits).
The number represented is essentially M * 2 ^ E, except
that the exponent is offset by a bias (e=1023) such that
the bit pattern is always non-negative. The actual value
is (-1)^S * M * 2^(E-e).
The mantissa/exponent representation is ambiguous, as
doubling the mantissa can be compensated by decreasing
the exponent by one and vice versa. When an IEEE 754
number is stored with its 52-bit mantissa left-shifted
such that there are no leading zero bits (and the exponent
adjusted accordingly), it is said to be normalized.
Because the high-order bit of the mantissa is then always
one, it is implicitly assumed but not actually stored:
the mantissa has the form M = 1.F where F is the 52
stored bits. This gains an additional bit of precision.
Extremely small (in magnitude) numbers with exponent -1022 are called subnormal and are stored un-normalized, that is, with a mantissa that can contain leading zero bits. This way an underflow to zero is delayed at the price of diminishing precision.
| S | E | F | Value |
|---|---|---|---|
| any | 1..2046 | any | (-1)^S * 2^(E-1023) * 1.F |
| any | 0 | nonzero | (-1)^S * 2^-1022 * 0.F |
| 0 | 0 | 0 | +0 |
| 1 | 0 | 0 | -0 |
| 0 | 2047 | 0 | +infty |
| 1 | 2047 | 0 | -infty |
| any | 2047 | nonzero | NaN |
The first line in the table stands for normalized numbers. The second line is for “subnormal” (non-normalized) numbers. Both positive and negative zero are treated the same in computations. NaN stands for “Not a Number” and has the property that it is not equal to any value, including NaN.
Collection of my simple and miniature tools.
Copyright (C) 1999-2008 Urs Jakob Ruetschi
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
