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string(3tcl) Tcl Built-In Commands string(3tcl) 





NAME


string - Manipulate strings






SYNOPSIS


string option arg ?arg ...?








DESCRIPTION


Performs one of several string operations, depending on
    option. The legal options (which may be abbreviated) are:



  

  
Concatenate the given strings just like placing them directly next
      to each other and return the resulting compound string. If no
      strings are present, the result is an empty string.






This primitive is occasionally handier than juxtaposition of
    strings when mixed quoting is wanted, or when the aim is to return the
    result of a concatenation without resorting to return -level
    0, and is more efficient than building a list of arguments and using
    join with an empty join string.





  

  
Perform a character-by-character comparison of strings string1 and
      string2. Returns -1, 0, or 1, depending on whether string1
      is lexicographically less than, equal to, or greater than string2.
      If -length is specified, then only the first length
      characters are used in the comparison. If -length is negative, it
      is ignored. If -nocase is specified, then the strings are compared
      in a case-insensitive manner.

  

  
Perform a character-by-character comparison of strings string1 and
      string2. Returns 1 if string1 and string2 are
      identical, or 0 when not. If -length is specified, then only the
      first length characters are used in the comparison. If
      -length is negative, it is ignored. If -nocase is specified,
      then the strings are compared in a case-insensitive manner.

  

  
Search haystackString for a sequence of characters that exactly
      match the characters in needleString. If found, return the index of
      the first character in the first such match within haystackString.
      If not found, return -1. If startIndex is specified (in any of the
      forms described in STRING INDICES), then the search is constrained
      to start with the character in haystackString specified by the
      index. For example,










string first a 0a23456789abcdef 5




will return 10, but






string first a 0123456789abcdef 11




will return -1.





  

  
Returns the charIndex'th character of the string argument. A
      charIndex of 0 corresponds to the first character of the string.
      charIndex may be specified as described in the STRING
      INDICES section.






If charIndex is less than 0 or greater than or equal to the
    length of the string then this command returns an empty string.





  

  
Returns 1 if string is a valid member of the specified character
      class, otherwise returns 0. If -strict is specified, then an empty
      string returns 0, otherwise an empty string will return 1 on any class. If
      -failindex is specified, then if the function returns 0, the index
      in the string where the class was no longer valid will be stored in the
      variable named varname. The varname will not be set if
      string is returns 1. The following character classes are recognized
      (the class name can be abbreviated):







  

  
Any Unicode alphabet or digit character.

  

  
Any Unicode alphabet character.

  

  
Any character with a value less than \u0080 (those that are in the 7-bit
      ascii range).

  

  
Any of the forms allowed to Tcl_GetBoolean.

  

  
Any Unicode control character.

  

  
Any Unicode digit character. Note that this includes characters outside of
      the [0-9] range.

  

  
Any of the forms allowed to Tcl_GetDoubleFromObj.

  

  
Any of the valid string formats for an integer value of arbitrary size in
      Tcl, with optional surrounding whitespace. The formats accepted are
      exactly those accepted by the C routine Tcl_GetBignumFromObj.

  

  
Any of the forms allowed to Tcl_GetBoolean where the value is
      false.

  

  
Any Unicode printing character, except space.

  

  
Any of the valid string formats for a 32-bit integer value in Tcl, with
      optional surrounding whitespace. In case of overflow in the value, 0 is
      returned and the varname will contain -1.

  

  
Any proper list structure, with optional surrounding whitespace. In case
      of improper list structure, 0 is returned and the varname will
      contain the index of the “element” where the list parsing
      fails, or -1 if this cannot be determined.

  

  
Any Unicode lower case alphabet character.

  

  
Any Unicode printing character, including space.

  

  
Any Unicode punctuation character.

  

  
Any Unicode whitespace character, mongolian vowel separator (U+180e), zero
      width space (U+200b), word joiner (U+2060) or zero width no-break space
      (U+feff) (=BOM).

  

  
Any of the forms allowed to Tcl_GetBoolean where the value is
    true.

  

  
Any upper case alphabet character in the Unicode character set.

  

  
Any of the valid forms for a wide integer in Tcl, with optional
      surrounding whitespace. In case of overflow in the value, 0 is returned
      and the varname will contain -1.

  

  
Any Unicode word character. That is any alphanumeric character, and any
      Unicode connector punctuation characters (e.g. underscore).

  

  
Any hexadecimal digit character ([0-9A-Fa-f]).




In the case of boolean, true and false, if
    the function will return 0, then the varname will always be set to 0,
    due to the varied nature of a valid boolean value.





  

  
Search haystackString for a sequence of characters that exactly
      match the characters in needleString. If found, return the index of
      the first character in the last such match within haystackString.
      If there is no match, then return -1. If lastIndex is specified (in
      any of the forms described in STRING INDICES), then only the
      characters in haystackString at or before the specified
      lastIndex will be considered by the search. For example,










string last a 0a23456789abcdef 15




will return 10, but






string last a 0a23456789abcdef 9




will return 1.





  

  
Returns a decimal string giving the number of characters in string.
      Note that this is not necessarily the same as the number of bytes used to
      store the string. If the value is a byte array value (such as those
      returned from reading a binary encoded channel), then this will return the
      actual byte length of the value.

  

  
Replaces substrings in string based on the key-value pairs in
      mapping. mapping is a list of key value key value ...
      as in the form returned by array get. Each instance of a key in the
      string will be replaced with its corresponding value. If -nocase is
      specified, then matching is done without regard to case differences. Both
      key and value may be multiple characters. Replacement is
      done in an ordered manner, so the key appearing first in the list will be
      checked first, and so on. string is only iterated over once, so
      earlier key replacements will have no affect for later key matches. For
      example,










string map {abc 1 ab 2 a 3 1 0} 1abcaababcabababc




will return the string 01321221.


Note that if an earlier key is a prefix of a later one, it
    will completely mask the later one. So if the previous example is reordered
    like this,






string map {1 0 ab 2 a 3 abc 1} 1abcaababcabababc




it will return the string 02c322c222c.





  

  
See if pattern matches string; return 1 if it does, 0 if it
      does not. If -nocase is specified, then the pattern attempts to
      match against the string in a case insensitive manner. For the two strings
      to match, their contents must be identical except that the following
      special sequences may appear in pattern:







  
*

  
Matches any sequence of characters in string, including a null
      string.

  
?

  
Matches any single character in string.

  
[chars]

  
Matches any character in the set given by chars. If a sequence of
      the form x-y appears in chars, then any
      character between x and y, inclusive, will match. When used
      with -nocase, the end points of the range are converted to lower
      case first. Whereas {[A-z]} matches “_” when matching
      case-sensitively (since “_” falls between the
      “Z” and “a”), with -nocase this is
      considered like {[A-Za-z]} (and probably what was meant in the first
      place).

  

  
Matches the single character x. This provides a way of avoiding the
      special interpretation of the characters *?[]\ in
    pattern.







  

  
Returns a range of consecutive characters from string, starting
      with the character whose index is first and ending with the
      character whose index is last. An index of 0 refers to the first
      character of the string. first and last may be specified as
      for the index method. If first is less than zero then it is
      treated as if it were zero, and if last is greater than or equal to
      the length of the string then it is treated as if it were end. If
      first is greater than last then an empty string is
    returned.

  

  
Returns string repeated count number of times.

  

  
Removes a range of consecutive characters from string, starting
      with the character whose index is first and ending with the
      character whose index is last. An index of 0 refers to the first
      character of the string. First and last may be specified as
      for the index method. If newstring is specified, then it is
      placed in the removed character range. If first is less than zero
      then it is treated as if it were zero, and if last is greater than
      or equal to the length of the string then it is treated as if it were
      end. The initial string is returned untouched, if first is
      greater than last, or if first is equal to or greater than
      the length of the initial string, or last is less than 0.

  

  
Returns a string that is the same length as string but with its
      characters in the reverse order.

  

  
Returns a value equal to string except that all upper (or title)
      case letters have been converted to lower case. If first is
      specified, it refers to the first char index in the string to start
      modifying. If last is specified, it refers to the char index in the
      string to stop at (inclusive). first and last may be
      specified using the forms described in STRING INDICES.

  

  
Returns a value equal to string except that the first character in
      string is converted to its Unicode title case variant (or upper
      case if there is no title case variant) and the rest of the string is
      converted to lower case. If first is specified, it refers to the
      first char index in the string to start modifying. If last is
      specified, it refers to the char index in the string to stop at
      (inclusive). first and last may be specified using the forms
      described in STRING INDICES.

  

  
Returns a value equal to string except that all lower (or title)
      case letters have been converted to upper case. If first is
      specified, it refers to the first char index in the string to start
      modifying. If last is specified, it refers to the char index in the
      string to stop at (inclusive). first and last may be
      specified using the forms described in STRING INDICES.

  

  
Returns a value equal to string except that any leading or trailing
      characters present in the string given by chars are removed. If
      chars is not specified then white space is removed (any character
      for which string is space returns 1, and "\0").

  

  
Returns a value equal to string except that any leading characters
      present in the string given by chars are removed. If chars
      is not specified then white space is removed (any character for which
      string is space returns 1, and "\0").

  

  
Returns a value equal to string except that any trailing characters
      present in the string given by chars are removed. If chars
      is not specified then white space is removed (any character for which
      string is space returns 1, and "\0").






OBSOLETE SUBCOMMANDS


These subcommands are currently supported, but are likely to go
    away in a future release as their functionality is either virtually never
    used or highly misleading.



  

  
Returns a decimal string giving the number of bytes used to represent
      string in memory when encoded as Tcl's internal modified UTF-8; Tcl
      may use other encodings for string as well, and does not guarantee
      to only use a single encoding for a particular string. Because
      UTF-8 uses a variable number of bytes to represent Unicode characters, the
      byte length will not be the same as the character length in general. The
      cases where a script cares about the byte length are rare.






In almost all cases, you should use the string length
    operation (including determining the length of a Tcl byte array value).
    Refer to the Tcl_NumUtfChars manual entry for more details on the
    UTF-8 representation.


Formally, the string bytelength operation returns the
    content of the length field of the Tcl_Obj structure, after
    calling Tcl_GetString to ensure that the bytes field is
    populated. This is highly unlikely to be useful to Tcl scripts, as Tcl's
    internal encoding is not strict UTF-8, but rather a modified CESU-8 with a
    denormalized NUL (identical to that used in a number of places by Java's
    serialization mechanism) to enable basic processing with non-Unicode-aware C
    functions. As this representation should only ever be used by Tcl's
    implementation, the number of bytes used to store the representation is of
    very low value (except to C extension code, which has direct access for the
    purpose of memory management, etc.)


Compatibility note: it is likely that this subcommand will
    be withdrawn in a future version of Tcl. It is better to use the encoding
    convertto command to convert a string to a known encoding and then apply
    string length to that.






string length [encoding convertto utf-8 $theString]







  

  
Returns the index of the character just after the last one in the word
      containing character charIndex of string. charIndex
      may be specified using the forms in STRING INDICES. A word is
      considered to be any contiguous range of alphanumeric (Unicode letters or
      decimal digits) or underscore (Unicode connector punctuation) characters,
      or any single character other than these.

  

  
Returns the index of the first character in the word containing character
      charIndex of string. charIndex may be specified using
      the forms in STRING INDICES. A word is considered to be any
      contiguous range of alphanumeric (Unicode letters or decimal digits) or
      underscore (Unicode connector punctuation) characters, or any single
      character other than these.










STRING INDICES


When referring to indices into a string (e.g., for string
    index or string range) the following formats are supported:



  

  
For any index value that passes string is integer -strict, the char
      specified at this integral index (e.g., 2 would refer to the
      “c” in “abcd”).

  

  
The last char of the string (e.g., end would refer to the
      “d” in “abcd”).

  

  
The last char of the string minus the specified integer offset N
      (e.g., “end-1” would refer to the “c”
      in “abcd”).

  

  
The last char of the string plus the specified integer offset N
      (e.g., “end+-1” would refer to the “c”
      in “abcd”).

  

  
The char specified at the integral index that is the sum of integer values
      M and N (e.g., “1+1” would refer to the
      “c” in “abcd”).

  

  
The char specified at the integral index that is the difference of integer
      values M and N (e.g., “2-1” would refer
      to the “b” in “abcd”).




In the specifications above, the integer value M contains
    no trailing whitespace and the integer value N contains no leading
    whitespace.






EXAMPLE


Test if the string in the variable string is a proper
    non-empty prefix of the string foobar.






set length [string length $string]
if {$length == 0} {


    set isPrefix 0
} else {


    set isPrefix [string equal -length $length $string "foobar"]
}








SEE ALSO


expr(3tcl), list(3tcl)






KEYWORDS


case conversion, compare, index, match, pattern, string, word,
    equal, ctype, character, reverse







  

    8.1
    Tcl