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StringExpression
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StringExpression

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s1~~s2~~… or StringExpression[s1,s2,…]

represents a sequence of strings and symbolic string objects si.

Details

  • "str1"~~"str2"~~… yields an ordinary string obtained by concatenating the characters in the "stri".
  • The following objects can appear in StringExpression:
  • "string"a literal string of characters
    _any single character
    __any substring of one or more characters
    ___any substring of zero or more characters
    x_, x__, x___ substrings given the name x
    x:patternpattern given the name x
    pattern..pattern repeated one or more times
    pattern...pattern repeated zero or more times
    {patt1,patt2,…} or patt1|patt2|…a pattern matching at least one of the patti
    AnyOrder[patt1, patt2, …]a pattern matching all of the patti in any order
    FixedOrder[patt1, patt2, …]a pattern matching the concatenation of the patti
    patt/;conda pattern for which cond evaluates to True
    pattern?testa pattern for which test yields True for each character
    Whitespacea sequence of whitespace characters
    NumberStringthe characters of a number
    DatePattern[spec]the characters of a date
    charobjan object representing a character class (see below)
    RegularExpression["regexp"]substring matching a regular expression
    StringExpression[…]an arbitrary string expression
  • The following represent classes of characters:
  • {c1,c2,…}any of the "ci"
    Characters["c1c2…"]any of the "ci"
    CharacterRange["c1","c2"]any character in the range "c1" to "c2"
    HexadecimalCharacterhexadecimal digit 0-9, a-f, A-F
    DigitCharacterdigit 0–9
    LetterCharacterletter
    WhitespaceCharacterspace, newline, tab, or other whitespace character
    WordCharacterletter or digit
    Except[p]any character except ones matching p
  • The following represent positions in strings:
  • StartOfStringstart of the whole string
    EndOfStringend of the whole string
    StartOfLinestart of a line
    EndOfLineend of a line
    WordBoundaryboundary between word characters and others
    Except[WordBoundary]anywhere except a word boundary
  • When constructs like __ or .. are present, there may be several different ways in which a given StringExpression can match a particular string.
  • By default, the Wolfram Language will use the one that makes pattern elements that appear earlier in the StringExpression match the longest possible substrings.
  • The following determine which match will be used if there are several possibilities:
  • Shortest[p]the shortest consistent match for p
    Longest[p]the longest consistent match for p (default)
  • In matching ordinary expressions instead of strings, the shortest instead of the longest consistent match is used.
  • StringExpression objects can be used in many string manipulation functions, including StringReplace, StringCases, StringSplit, and StringMatchQ.
  • StringExpression has attributes Flat and OneIdentity.

Examples

open allclose all

Basic Examples  (2)Summary of the most common use cases

A string expression representing the string "ab" followed by any single character:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-bveo8n
Out[1]=1

This makes a replacement for each occurrence of the string pattern "ab"~~__:

In[2]:=2
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https://wolfram.com/xid/0enwfnclu-7ieuh3
Out[2]=2

Give all pairs of identical characters in the string:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-3hq213
Out[1]=1

Scope  (5)Survey of the scope of standard use cases

A single blank (_) stands for any single character:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-g4bgre
Out[1]=1

Double blank (__) stands for any sequence of one or more characters:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-ncfuy6
Out[1]=1

Triple blank (___) stands for any sequence of zero or more characters:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-b9f5di
Out[1]=1

Use AnyOrder to match patterns in any order:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-ed28t9
Out[1]=1

Assigning a matching AnyOrder to a variable preserves the order in the string:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-j998vg
Out[1]=1

Applications  (1)Sample problems that can be solved with this function

Find the primes with four identical digits:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-cyghu7
Out[1]=1

By converting to strings, you can use StringMatchQ:

In[2]:=2
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https://wolfram.com/xid/0enwfnclu-fe0f4p
Out[2]=2

Properties & Relations  (1)Properties of the function, and connections to other functions

StringExpression objects can be used in many string manipulation functions:

In[1]:=1
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https://wolfram.com/xid/0enwfnclu-dd8kms
Out[1]=1
In[2]:=2
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https://wolfram.com/xid/0enwfnclu-d55aq2
Out[2]=2
In[3]:=3
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https://wolfram.com/xid/0enwfnclu-i97mix
Out[3]=3
In[4]:=4
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https://wolfram.com/xid/0enwfnclu-jszhv7
Out[4]=4
In[5]:=5
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https://wolfram.com/xid/0enwfnclu-qhl02a
Out[5]=5
In[6]:=6
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https://wolfram.com/xid/0enwfnclu-eoefc4
Out[6]=6
In[7]:=7
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https://wolfram.com/xid/0enwfnclu-z8122m
Out[7]=7
In[8]:=8
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https://wolfram.com/xid/0enwfnclu-ltlu86
Out[8]=8
Wolfram Research (2004), StringExpression, Wolfram Language function, https://reference.wolfram.com/language/ref/StringExpression.html (updated 2014).
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Wolfram Research (2004), StringExpression, Wolfram Language function, https://reference.wolfram.com/language/ref/StringExpression.html (updated 2014).

Text

Wolfram Research (2004), StringExpression, Wolfram Language function, https://reference.wolfram.com/language/ref/StringExpression.html (updated 2014).

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Wolfram Research (2004), StringExpression, Wolfram Language function, https://reference.wolfram.com/language/ref/StringExpression.html (updated 2014).

CMS

Wolfram Language. 2004. "StringExpression." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2014. https://reference.wolfram.com/language/ref/StringExpression.html.

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Wolfram Language. 2004. "StringExpression." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2014. https://reference.wolfram.com/language/ref/StringExpression.html.

APA

Wolfram Language. (2004). StringExpression. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/StringExpression.html

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Wolfram Language. (2004). StringExpression. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/StringExpression.html

BibTeX

@misc{reference.wolfram_2025_stringexpression, author="Wolfram Research", title="{StringExpression}", year="2014", howpublished="\url{https://reference.wolfram.com/language/ref/StringExpression.html}", note=[Accessed: 25-March-2025 ]}

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@misc{reference.wolfram_2025_stringexpression, author="Wolfram Research", title="{StringExpression}", year="2014", howpublished="\url{https://reference.wolfram.com/language/ref/StringExpression.html}", note=[Accessed: 25-March-2025 ]}

BibLaTeX

@online{reference.wolfram_2025_stringexpression, organization={Wolfram Research}, title={StringExpression}, year={2014}, url={https://reference.wolfram.com/language/ref/StringExpression.html}, note=[Accessed: 25-March-2025 ]}

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@online{reference.wolfram_2025_stringexpression, organization={Wolfram Research}, title={StringExpression}, year={2014}, url={https://reference.wolfram.com/language/ref/StringExpression.html}, note=[Accessed: 25-March-2025 ]}