Let us first look at the two special symbols '^' and '$'. Their role is to point out the beginning and end of a string. The example is as follows:
"^ The": indicates all strings starting with "THE" ("there", "the cat", etc.);
"of despair $": indicates the string ending with "of despair";
"^ ABC $": Indicates that the start and end are string of "abc" - huh, only "ABC";
"Notice": indicates any string containing "Notice".
The last example, if you don't use two special characters, you are in any part of the string you want to find - you and
Do not position it on a top.
Others have the three symbols of '*', ' ' and '' ', indicating that one or a sequence character is repeated. They represent "no or
More "," once or more "and" no or once ". Below is a few examples:
"ab *": means a string having a A back followed by zero or several b. ("A", "ab", "abbb", ...);
"ab ": means that a string has a A back follows at least one B or more;
"ab?": Indicates a string having a A back followed by zero or one B;
"a? b $": indicates that there is zero or one A follow one or more b at the end of the string.
You can also use the scope, enclose with braces to indicate the range of repetitions.
"AB {2}": means a string has a A follow 2 B ("ABB");
"AB {2,}": means a string having a A follow at least 2 b;
"AB {3, 5}": indicates a string having a A followed 3 to 5 B.
Note that you must specify the lower limit of the range (such as "{0, 2}" instead of "{, 2}"). Also, you may notice, '*', ' ' and
'?' Is equivalent to "{0,}", "{1,}" and "{0, 1}".
There is also a '|', indicating "or" operation:
"hi & brvbarhello": indicates that there is "hi" or "hello" in a string;
"(B & Brvbarcd) EF": means "bef" or "cdef";
"(A & Brvbarb) * C": Represents a string of "a" "b" mixed strings and one "c";
'.' Can replace any character:
"a. [0-9]": indicates a string having a "A" behind follows an arbitrary character and a number;
"^. {3} $": Indicates a string (length of 3 characters); square brackets indicate that some characters are allowed to appear in a particular location in a string:
"[ab]": indicates a string having a "a" or "b" (equivalent to "a & brvbarb");
"[A-D]": means a string contains a lower-write 'a' into 'd' (equivalent to "A & Brvbarb & Brvbarc & Brvbard" or "[ABCD]");
"^ [A-ZA-Z]": indicates a string that starts with letters;
"[0-9]%": indicates a number before a percent sign;
", [A-ZA-Z0-9] $": Indicates that a string is followed by a comma with a letter or numbers.
You can also use '^' in square brackets to indicate the characters that do not want to appear, '^' should in square brackets. (Such as "% [^ a-za-z]%" table
Letters should not appear in two percent signs).
In order to express verbatics, you must add transfer characters '/' before "^. $ () | * ? {/".
Please note that in square brackets, no escape characters need.
