04-16-2010
Arithmetic expressions in modern shells use the same syntax as is used in the C programming language. And in C, the value of a numeric expression using the comma operator is the value of the last subexpression, in your case 15 - 4 .
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I am trying to understand
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LEARN ABOUT DEBIAN
numgrep
NUMGREP(1) User Contributed Perl Documentation NUMGREP(1)
NAME
numgrep - This program is the numeric equivilent of the grep utility.
SYNOPSIS
numgrep [-dhlV] <FILE>
| numgrep [-dhlV] (Input on STDIN from pipeline.)
numgrep [-dhlV] (Input on STDIN. Use Ctrl-D to stop.)
DESCRIPTION
numgrep searches for different occurances of numbers through the use of numeric expressions.
OPTIONS
-l Print the matching numbers out one per line
instead of printing the entire line they are on.
-h Help: You're looking at it.
-V Increase verbosity.
-d Debug mode. For developers
EXPRESSIONS
numgrep uses a special numeric expression matching system. Basically, it searches for ranges, factors and sequences of numbers. Here is a
list of the syntax characters and some sample expressions that will get you going:
/<expression>/
Put your expression or set of expressions between these
two forward slashes.
.. Range expression. A number must be used on the left
and/or right of this expression to specify that numbers
between, greater than or less than the numbers specified
should be matched.
, Expression sepeartor. The comma sepearates one complete
expression from another in a set enclosed by //.
m<n> Multiples of <n>. This operator, followed by a number
<n> will match any number <x> that is an integer
multiple of <n>. Meaning that <x> = <n> times <y>,
where <y> is any integer.
f<n> Factors of <n>. This operator, followed by a number <n>
will match any number <x> that is an integer factor of
<n>. Meaning that <x> = <n> divided by <y>, where <y>
is any integer.
NOTE: Checking for factors and multiples is very fast because it
is checked by doing a single modulus operation on two numbers.
Examples:
/2..10/ Match any number between 2 and 10.
/2..10,20..30/ Match any number between 2 and 10 or between 20 and 30.
/56,34,512,45,67/ Match any of the numbers 56, 34, 512, 45 or 67.
/m3/ Match any integer that is a multiple of 3.
/f1024/ Match any integer that is a factor of 1024.
$ numrange -N /1..1000/ | numgrep /f1024/
1
2
4
8
16
32
64
128
256
512
$
BUGS
numgrep can't handle certain situations properly. Such as if it encounters a number with leading zeros, it will treat it as an octal
number and thus might not match the way you would expect.
numgrep does not yet allow you to mix numbers and text in the matching expression. So you can not do something like 'numgrep
/port=0..1023/ firewall.log'. But this will be changed in the future.
SEE ALSO
numaverage(1), numbound(1), numinterval(1), numnormalize(1), numprocess(1), numsum(1), numrandom(1), numrange(1), numround(1)
COPYRIGHT
numgrep is part of the num-utils package, which is copyrighted by Suso Banderas and released under the GPL license. Please read the
COPYING and LICENSE files that came with the num-utils package
Developers can read the GOALS file and contact me about providing
submitions or help for the project.
BUGS
numgrep will round decimal numbers with more than 15 digits of accuracy. This is
mostly due to limit's in the way programming languages deal directly with numbers.
MORE INFO
More info on numgrep can be found at:
http://suso.suso.org/programs/num-utils/
perl v5.10.1 2009-10-31 NUMGREP(1)