Provided by: tcl8.6-doc_8.6.14+dfsg-1build1_all 
NAME
string - Manipulate strings
SYNOPSIS
string option arg ?arg ...?
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DESCRIPTION
Performs one of several string operations, depending on option. The legal options (which may be
abbreviated) are:
string cat ?string1? ?string2...?
Concatenate the given strings just like placing them directly next to each other and return the 2
resulting compound string. If no strings are present, the result is an empty string. 2
This primitive is occasionally handier than juxtaposition of strings when mixed quoting is wanted, 2
or when the aim is to return the result of a concatenation without resorting to return -level 0, 2
and is more efficient than building a list of arguments and using join with an empty join string. 2
string compare ?-nocase? ?-length length? string1 string2
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.
string equal ?-nocase? ?-length length? string1 string2
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.
string first needleString haystackString ?startIndex?
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.
string index string charIndex
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.
string is class ?-strict? ?-failindex varname? 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):
alnum Any Unicode alphabet or digit character.
alpha Any Unicode alphabet character.
ascii Any character with a value less than \u0080 (those that are in the 7-bit ascii range).
boolean Any of the forms allowed to Tcl_GetBoolean.
control Any Unicode control character.
digit Any Unicode digit character. Note that this includes characters outside of the [0-9]
range.
double Any of the forms allowed to Tcl_GetDoubleFromObj.
entier Any of the valid string formats for an integer value of arbitrary size in Tcl, with 2
optional surrounding whitespace. The formats accepted are exactly those accepted by 2
the C routine Tcl_GetBignumFromObj.
false Any of the forms allowed to Tcl_GetBoolean where the value is false.
graph Any Unicode printing character, except space.
integer 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.
list 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.
lower Any Unicode lower case alphabet character.
print Any Unicode printing character, including space.
punct Any Unicode punctuation character.
space 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).
true Any of the forms allowed to Tcl_GetBoolean where the value is true.
upper Any upper case alphabet character in the Unicode character set.
wideinteger 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.
wordchar Any Unicode word character. That is any alphanumeric character, and any Unicode
connector punctuation characters (e.g. underscore).
xdigit 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.
string last needleString haystackString ?lastIndex?
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.
string length string
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.
string map ?-nocase? mapping string
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.
string match ?-nocase? pattern string
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).
\x Matches the single character x. This provides a way of avoiding the special
interpretation of the characters *?[]\ in pattern.
string range string first last
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.
string repeat string count
Returns string repeated count number of times.
string replace string first last ?newstring?
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.
string reverse string
Returns a string that is the same length as string but with its characters in the reverse order.
string tolower string ?first? ?last?
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.
string totitle string ?first? ?last?
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.
string toupper string ?first? ?last?
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.
string trim string ?chars?
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").
string trimleft string ?chars?
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").
string trimright string ?chars?
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.
string bytelength string
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]
string wordend string charIndex
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.
string wordstart string charIndex
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:
integer 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”).
end The last char of the string (e.g., end would refer to the “d” in “abcd”).
end-N The last char of the string minus the specified integer offset N (e.g., “end-1” would refer to
the “c” in “abcd”).
end+N The last char of the string plus the specified integer offset N (e.g., “end+-1” would refer to
the “c” in “abcd”).
M+N 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”).
M-N 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
Tcl 8.1 string(3tcl)