string(n) Tcl Built-In Commands string(n) ______________________________________________________________________________
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:
string cat ?string1? ?string2...?
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. |
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 optional surrounding |
whitespace. The formats accepted are exactly those |
accepted by 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 (using the forms described in
STRING INDICES). An index of 0 refers to the first character of
the string; an index of end refers to last 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 a string consisting of string concatenated with itself
count times. If count is 0, the empty string will be returned.
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 (using the forms described in
STRING INDICES). 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 not specified, only the character
at position first is converted, otherwise last 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 not specified, only the character at
position first is converted, otherwise last 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 not specified, only the character
at position first is converted, otherwise last 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(n), list(n)
KEYWORDS
case conversion, compare, index, integer value, match, pattern, string,
word, equal, ctype, character, reverse
Tcl 8.1 string(n)
tcl 8.6.17 - Generated Thu Aug 21 10:04:00 CDT 2025