| pattern | finds |
|---|---|
| ring | ring rings bring string engineering Springer cringe etc. |
| \bring | ring rings (but not: bring engineering Springer or string) |
| ring\b | ring bring string engineering (but not: rings or Springer) |
| \bring\b | ring Ring RING (but not: rings bring etc.) |
| algebraic sy | algebraic systems algebraic symbols etc. |
| modu|gauss | unimodular Gauss gaussian etc. (no spaces around "|" ) |
The more complicated pattern:
pattern1 = \blie\b pattern2 = represent|algebr|cohomol|deformlocates all books with " lie " and any of "represent", "algebr", "cohomol", or "deform" in their title or as their subject ("\blie\b" means that "lie" appears as a separate word, excluding words like "applied").
If you also enter a second pattern, the (faster) search will
match only if both patterns are found. For instance if the
first pattern is riemann and the second pattern is
geometry , then it will only match entries in which both
riemann AND geometry occur somewhere
This runs faster if the least likely pattern is placed first.
Thus, riemann AND geometry runs faster than
geometry AND riemann.
A Fuzzy Search (click "fuzzy button")
permits 1 character not to match. Useful for accents.
Example: Kahler also matches Kähler,
Kaehler, and Khler.
For a fuzzy search that allows 2 errors in the pattern use:
poincar and hler might be
used for Poincaré or Kähler.
EXPERTS: These are gnu egrep "regular expression" patterns (fuzzy searches use agrep). Here are most of the details from the man page (see above for examples).
A regular expression is a pattern that describes a set of
strings. Regular expressions are constructed analogously
to arithmetic expressions, by using various operators to
combine smaller expressions.
Grep understands two different versions of regular expres-
sion syntax: ``basic'' and ``extended.'' In GNU grep,
there is no difference in available functionality using
either syntax. In other implementations, basic regular
expressions are less powerful. The following description
applies to extended regular expressions; differences for
basic regular expressions are summarized afterwards.
The fundamental building blocks are the regular expres-
sions 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 list of characters enclosed by [ and ] matches any sin-
gle 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. A range of ASCII
characters may be specified by giving the first and last
characters, separated by a hyphen. Finally, certain named
classes of characters are predefined. 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 is dependent upon the ASCII character encoding,
whereas the former is portable. (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 lit-
eral - 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 operators:
? 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.
{,m} The preceding item is optional and is matched at
most m 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 concate-
nating two substrings that respectively match the concate-
nated subexpressions.
Two regular expressions may be joined by the infix opera-
tor |; the resulting regular expression matches any string
matching either subexpression.
Repetition takes precedence over concatenation, which in
turn takes precedence over alternation. A whole subex-
pression 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 regular expression.
In basic regular expressions the metacharacters ?, +, {,
|, (, and ) lose their special meaning; instead use the
backslashed versions \?, \+, \{, \|, \(, and \).
In egrep the metacharacter { loses its special meaning;
instead use \{.