String Patterns
An important feature of string manipulation functions like
StringReplace is that they handle not only literal strings but also patterns for collections of strings.
This replaces any character by u.
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You can specify patterns for strings by using
string expressions that contain ordinary strings mixed with
Mathematica symbolic pattern objects.
s_{1}~~s_{2}~~... or StringExpression[s_{1},s_{2},...] 
 a sequence of strings and pattern objects 
String expressions.
Here is a string expression that represents the string ab followed by any single character.
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This makes a replacement for each occurrence of the string pattern.
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StringMatchQ["s",patt]  test whether "s" matches patt 
StringFreeQ["s",patt]  test whether "s" is free of substrings matching patt 
StringCases["s",patt]  give a list of the substrings of "s" that match patt 
StringCases["s",lhs>rhs]  replace each case of lhs by rhs 
StringPosition["s",patt]  give a list of the positions of substrings that match patt 
StringCount["s",patt]  count how many substrings match patt 
StringReplace["s",lhs>rhs]  replace every substring that matches lhs 
StringReplaceList["s",lhs>rhs] 
 give a list of all ways of replacing lhs 
StringSplit["s",patt]  split s at every substring that matches patt 
StringSplit["s",lhs>rhs]  split at lhs, inserting rhs in its place 
Functions that support string patterns.
This gives all cases of the pattern that appear in the string.
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This gives each character that appears after an "ab" string.
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This gives all pairs of identical characters in the string.
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You can use all the standard
Mathematica pattern objects in string patterns. Single blanks (
_) always stand for single characters. Double blanks (
__) stand for sequences of one or more characters.
Single blank ( _) stands for any single character.
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Double blank ( __) stands for any sequence of one or more characters.
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Triple blank ( ___) stands for any sequence of zero or more characters.
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"string"  a literal string of characters 
_  any single character 
__  any sequence of one or more characters 
___  any sequence of zero or more characters 
x_, x__, x___  substrings given the name x 
x:pattern  pattern given the name x 
pattern..  pattern repeated one or more times 
pattern...  pattern repeated zero or more times 
{patt_{1},patt_{2},...} or patt_{1}patt_{2}... 
 a pattern matching at least one of the patt_{i} 
patt/;cond  a pattern for which cond evaluates to True 
pattern?test  a pattern for which test yields True for each character 
Whitespace  a sequence of whitespace characters 
NumberString  the characters of a number 
charobj  an object representing a character class (see below) 
RegularExpression["regexp"]  substring matching a regular expression 
Objects in string patterns.
This splits at either a colon or semicolon.
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This finds all runs containing only a or b.
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Alternatives can be given in lists in string patterns.
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You can use standard
Mathematica constructs such as
Characters["c_{1}c_{2}..."] and
CharacterRange["c_{1}", "c_{2}"] to generate lists of alternative characters to use in string patterns.
This gives a list of characters.
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This replaces the vowel characters.
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This gives characters in the range "A" through "H".
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In addition to allowing explicit lists of characters,
Mathematica provides symbolic specifications for several common classes of possible characters in string patterns.
Specifications for classes of characters.
This picks out the digit characters in a string.
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This picks out all characters except digits.
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This picks out all runs of one or more digits.
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This converts the strings to numbers.
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String patterns are often used as a way to extract structure from strings of textual data. Typically this works by having different parts of a string pattern match substrings that correspond to different parts of the structure.
This picks out each = followed by a number.
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This extracts "variables" and "values" from the string.
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In many situations, textual data may contain sequences of spaces, newlines or tabs that should be considered "whitespace", and perhaps ignored. In
Mathematica, the symbol
Whitespace stands for any such sequence.
This removes all whitespace from the string.
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This replaces each sequence of spaces by a single comma.
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String patterns normally apply to substrings that appear at any position in a given string. Sometimes, however, it is convenient to specify that patterns can apply only to substrings at particular positions. You can do this by including symbols such as
StartOfString in your string patterns.
Constructs representing special positions in a string.
This replaces "a" wherever it appears in a string.
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This replaces "a" only when it immediately follows the start of a string.
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This replaces all occurrences of the substring "the".
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This replaces only occurrences that have a word boundary on both sides.
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String patterns allow the same kind of
/; and other conditions as ordinary
Mathematica patterns.
This gives cases of unequal successive characters in the string.
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When you give an object such as
x__ or
e.. in a string pattern,
Mathematica normally assumes that you want this to match the longest possible sequence of characters. Sometimes, however, you may instead want to match the shortest possible sequence of characters. You can specify this using
Shortest[p].
Longest[p]  the longest consistent match for p (default) 
Shortest[p]  the shortest consistent match for p 
Objects representing longest and shortest matches.
The string pattern by default matches the longest possible sequence of characters.
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Shortest specifies that instead the shortest possible match should be found.
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Mathematica by default treats characters such
"X" and
"x" as distinct. But by setting the option
IgnoreCase>True in string manipulation operations, you can tell
Mathematica to treat all such upper and lowercase letters as equivalent.
Specifying caseindependent string operations.
This replaces all occurrences of "the", independent of case.
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In some string operations, one may have to specify whether to include overlaps between substrings. By default
StringCases and
StringCount do not include overlaps, but
StringPosition does.
This picks out pairs of successive characters, by default omitting overlaps.
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Options for handling overlaps in strings.
This yields only a single match.
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This yields a succession of overlapping matches.
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This includes all possible overlapping matches.
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