A regular expression is a pattern that describes a set of strings.
Regular expressions are constructed analogously to arithmetic expres-
sions, by using various operators to combine smaller expressions.
grep understands three different versions of regular expression syntax:
"basic," "extended," and "perl." In GNU grep, there is no difference
in available functionality using either of the first two syntaxes. In
other implementations, basic regular expressions are less powerful.
The following description applies to extended regular expressions; dif-
ferences for basic regular expressions are summarized afterwards. Perl
regular expressions add additional functionality, but the implementa-
tion used here is undocumented and is not compatible with other grep
implementations.
The fundamental building blocks are the regular expressions that match
a single character. Most characters, including all letters and digits,
are regular expressions that match themselves. Any metacharacter with
special meaning may be quoted by preceding it with a backslash.
A bracket expression is a list of characters enclosed by [ and ]. It
matches any single character in that list; if the first character of
the list is the caret ^ then it matches any character not in the list.
For example, the regular expression [0123456789] matches any single
digit.
Within a bracket expression, a range expression consists of two charac-
ters separated by a hyphen. It matches any single character that sorts
between the two characters, inclusive, using the locale's collating
sequence and character set. For example, in the default C locale,
[a-d] is equivalent to [abcd]. Many locales sort characters in dictio-
nary order, and in these locales [a-d] is typically not equivalent to
[abcd]; it might be equivalent to [aBbCcDd], for example. To obtain
the traditional interpretation of bracket expressions, you can use the
C locale by setting the LC_ALL environment variable to the value C.
Finally, certain named classes of characters are predefined within
bracket expressions, as follows. Their names are self explanatory, and
they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:],
[:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:].
For example, [[:alnum:]] means [0-9A-Za-z], except the latter form
depends upon the C locale and the ASCII character encoding, whereas the
former is independent of locale and character set. (Note that the
brackets in these class names are part of the symbolic names, and must
be included in addition to the brackets delimiting the bracket list.)
Most metacharacters lose their special meaning inside lists. To
include a literal ] place it first in the list. Similarly, to include
a literal ^ place it anywhere but first. Finally, to include a literal
- place it last.
The period . matches any single character. The symbol \w is a synonym
for [[:alnum:]] and \W is a synonym for [^[:alnum]].
The caret ^ and the dollar sign $ are metacharacters that respectively
match the empty string at the beginning and end of a line. The symbols
\< and \> respectively match the empty string at the beginning and end
of a word. The symbol \b matches the empty string at the edge of a
word, and \B matches the empty string provided it's not at the edge of
a word.
A regular expression may be followed by one of several repetition oper-
ators:
? The preceding item is optional and matched at most once.
* The preceding item will be matched zero or more times.
+ The preceding item will be matched one or more times.
{n} The preceding item is matched exactly n times.
{n,} The preceding item is matched n or more times.
{n,m} The preceding item is matched at least n times, but not more
than m times.
Two regular expressions may be concatenated; the resulting regular
expression matches any string formed by concatenating two substrings
that respectively match the concatenated subexpressions.
Two regular expressions may be joined by the infix operator |; the
resulting regular expression matches any string matching either subex-
pression.
Repetition takes precedence over concatenation, which in turn takes
precedence over alternation. A whole subexpression may be enclosed in
parentheses to override these precedence rules.
The backreference \n, where n is a single digit, matches the substring
previously matched by the nth parenthesized subexpression of the regu-
lar expression.
In basic regular expressions the metacharacters ?, +, {, |, (, and )
lose their special meaning; instead use the backslashed versions \?,
\+, \{, \|, \(, and \).
Traditional egrep did not support the { metacharacter, and some egrep
implementations support \{ instead, so portable scripts should avoid {
in egrep patterns and should use [{] to match a literal {.
GNU egrep attempts to support traditional usage by assuming that { is
not special if it would be the start of an invalid interval specifica-
tion. For example, the shell command egrep '{1' searches for the two-
character string {1 instead of reporting a syntax error in the regular
expression. POSIX.2 allows this behavior as an extension, but portable
scripts should avoid it.
SMBus는 예전에는 안보였는데, 어느샌가 부터 야곰야곰 보이기 시작한 녀석이다.
눈에 띄기 시작한건 아마도.. 2기가 급이 넘어 가면서 부터였던것 같다.(노트북 제외)
그냥 머하는건지 BUS인가 보다 넘어 갔는데 문득 호기심이 발동하였다.
I2C 처럼 BUS 방식의 시리얼 통신이고, 전원관리 칩들, 온도, 팬 , 전압 센서등 연결하고 있다고 한다.
예전 같으면 BIOS에서 cpu / chasis / system 온도계 3개만 지원했는데 비해서
요즘에는 센서들이 너무 많아서 일일이 하나의 GPIO를 할당하기에는 무리가 있어서 BUS로 돌렸나보다.
The System Management Bus (abbreviated to SMBus or SMB) is
a simple two-wire bus, derived from I²C and used for communication with low-bandwidth
devices on a motherboard,
especially power related chips such as a laptop's rechargeable battery subsystem
(see Smart Battery
Data). Other devices might include temperature, fan or voltage sensors, lid
switches and clock chips. PCI add-in cards may connect to an SMBus segment
The SMBus was defined by Intel in 1995. It carries clock, data, and instructions
and is based on Philips' I²C serial bus
protocol. Its clock frequency range is 10 kHz to 100 kHz. (PMBus extends this to
400 kHz.) Its voltage levels and timings are more strictly defined than those of
I²C, but devices belonging to the two systems are often successfully mixed on
the same bus.
In general, the I2C bus and SMBus are compatible, but there are some subtle
differences between the two that could cause some problems. The following table
summarizes the differences between the two buses.
np2-ultimatum.zip
