path: root/doc/string.n

.\"
.\" Copyright (c) 1993 The Regents of the University of California.
.\" Copyright (c) 1994-1996 Sun Microsystems, Inc.
.\"
.\" See the file "license.terms" for information on usage and redistribution
.\" of this file, and for a DISCLAIMER OF ALL WARRANTIES.
.\"
.TH string n 8.1 Tcl "Tcl Built-In Commands"
.so man.macros
.BS
.\" Note:  do not modify the .SH NAME line immediately below!
.SH NAME
string \- Manipulate strings
.SH SYNOPSIS
\fBstring \fIoption arg \fR?\fIarg ...?\fR
.BE
.SH DESCRIPTION
.PP
Performs one of several string operations, depending on \fIoption\fR.
The legal \fIoption\fRs (which may be abbreviated) are:
.TP
\fBstring cat\fR ?\fIstring1\fR? ?\fIstring2...\fR?
.VS 8.6.2
Concatenate the given \fIstring\fRs just like placing them directly
next to each other and return the resulting compound string.  If no
\fIstring\fRs are present, the result is an empty string.
.RS
.PP
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 \fBreturn\fR \fB\-level 0\fR,
and is more efficient than building a list of arguments and using
\fBjoin\fR with an empty join string.
.RE
.VE
.TP
\fBstring compare\fR ?\fB\-nocase\fR? ?\fB\-length\fI length\fR? \fIstring1 string2\fR
.
Perform a character-by-character comparison of strings \fIstring1\fR
and \fIstring2\fR.  Returns \-1, 0, or 1, depending on whether
\fIstring1\fR is lexicographically less than, equal to, or greater
than \fIstring2\fR.  If \fB\-length\fR is specified, then only the
first \fIlength\fR characters are used in the comparison.  If
\fB\-length\fR is negative, it is ignored.  If \fB\-nocase\fR is
specified, then the strings are compared in a case-insensitive manner.
.TP
\fBstring equal\fR ?\fB\-nocase\fR? ?\fB\-length\fI length\fR? \fIstring1 string2\fR
.
Perform a character-by-character comparison of strings \fIstring1\fR
and \fIstring2\fR.  Returns 1 if \fIstring1\fR and \fIstring2\fR are
identical, or 0 when not.  If \fB\-length\fR is specified, then only
the first \fIlength\fR characters are used in the comparison.  If
\fB\-length\fR is negative, it is ignored.  If \fB\-nocase\fR is
specified, then the strings are compared in a case-insensitive manner.
.TP
\fBstring first \fIneedleString haystackString\fR ?\fIstartIndex\fR?
.
Search \fIhaystackString\fR for a sequence of characters that exactly match
the characters in \fIneedleString\fR.  If found, return the index of the
first character in the first such match within \fIhaystackString\fR.  If not
found, return \-1.  If \fIstartIndex\fR is specified (in any of the
forms described in \fBSTRING INDICES\fR), then the search is
constrained to start with the character in \fIhaystackString\fR specified by
the index.  For example,
.RS
.PP
.CS
\fBstring first a 0a23456789abcdef 5\fR
.CE
.PP
will return \fB10\fR, but
.PP
.CS
\fBstring first a 0123456789abcdef 11\fR
.CE
.PP
will return \fB\-1\fR.
.RE
.TP
\fBstring index \fIstring charIndex\fR
.
Returns the \fIcharIndex\fR'th character of the \fIstring\fR argument.
A \fIcharIndex\fR of 0 corresponds to the first character of the
string.  \fIcharIndex\fR may be specified as described in the
\fBSTRING INDICES\fR section.
.RS
.PP
If \fIcharIndex\fR is less than 0 or greater than or equal to the
length of the string then this command returns an empty string.
.RE
.TP
\fBstring is \fIclass\fR ?\fB\-strict\fR? ?\fB\-failindex \fIvarname\fR? \fIstring\fR
.
Returns 1 if \fIstring\fR is a valid member of the specified character
class, otherwise returns 0.  If \fB\-strict\fR is specified, then an
empty string returns 0, otherwise an empty string will return 1 on
any class.  If \fB\-failindex\fR 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 \fIvarname\fR.  The \fIvarname\fR
will not be set if \fBstring is\fR returns 1.  The following character
classes are recognized (the class name can be abbreviated):
.RS
.IP \fBalnum\fR 12
Any Unicode alphabet or digit character.
.IP \fBalpha\fR 12
Any Unicode alphabet character.
.IP \fBascii\fR 12
Any character with a value less than \eu0080 (those that are in the
7\-bit ascii range).
.IP \fBboolean\fR 12
Any of the forms allowed to \fBTcl_GetBoolean\fR.
.IP \fBcontrol\fR 12
Any Unicode control character.
.IP \fBdigit\fR 12
Any Unicode digit character.  Note that this includes characters
outside of the [0\-9] range.
.IP \fBdouble\fR 12
Any of the forms allowed to \fBTcl_GetDoubleFromObj\fR.
.IP \fBentier\fR 12
.VS 8.6
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 \fBTcl_GetBignumFromObj\fR.
.VE
.IP \fBfalse\fR 12
Any of the forms allowed to \fBTcl_GetBoolean\fR where the value is
false.
.IP \fBgraph\fR 12
Any Unicode printing character, except space.
.IP \fBinteger\fR 12
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 \fIvarname\fR will contain \-1.
.IP \fBlist\fR 12
Any proper list structure, with optional surrounding whitespace. In
case of improper list structure, 0 is returned and the \fIvarname\fR
will contain the index of the
.QW element
where the list parsing fails, or \-1 if this cannot be determined.
.IP \fBlower\fR 12
Any Unicode lower case alphabet character.
.IP \fBprint\fR 12
Any Unicode printing character, including space.
.IP \fBpunct\fR 12
Any Unicode punctuation character.
.IP \fBspace\fR 12
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).
.IP \fBtrue\fR 12
Any of the forms allowed to \fBTcl_GetBoolean\fR where the value is
true.
.IP \fBupper\fR 12
Any upper case alphabet character in the Unicode character set.
.IP \fBwideinteger\fR 12
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 \fIvarname\fR will contain \-1.
.IP \fBwordchar\fR 12
Any Unicode word character.  That is any alphanumeric character, and
any Unicode connector punctuation characters (e.g. underscore).
.IP \fBxdigit\fR 12
Any hexadecimal digit character ([0\-9A\-Fa\-f]).
.PP
In the case of \fBboolean\fR, \fBtrue\fR and \fBfalse\fR, if the
function will return 0, then the \fIvarname\fR will always be set to
0, due to the varied nature of a valid boolean value.
.RE
.TP
\fBstring last \fIneedleString haystackString\fR ?\fIlastIndex\fR?
.
Search \fIhaystackString\fR for a sequence of characters that exactly match
the characters in \fIneedleString\fR.  If found, return the index of the
first character in the last such match within \fIhaystackString\fR.  If there
is no match, then return \-1.  If \fIlastIndex\fR is specified (in any
of the forms described in \fBSTRING INDICES\fR), then only the
characters in \fIhaystackString\fR at or before the specified \fIlastIndex\fR
will be considered by the search.  For example,
.RS
.PP
.CS
\fBstring last a 0a23456789abcdef 15\fR
.CE
.PP
will return \fB10\fR, but
.PP
.CS
\fBstring last a 0a23456789abcdef 9\fR
.CE
.PP
will return \fB1\fR.
.RE
.TP
\fBstring length \fIstring\fR
.
Returns a decimal string giving the number of characters in
\fIstring\fR.  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.
.TP
\fBstring map\fR ?\fB\-nocase\fR? \fImapping string\fR
.
Replaces substrings in \fIstring\fR based on the key-value pairs in
\fImapping\fR.  \fImapping\fR is a list of \fIkey value key value ...\fR
as in the form returned by \fBarray get\fR.  Each instance of a
key in the string will be replaced with its corresponding value.  If
\fB\-nocase\fR is specified, then matching is done without regard to
case differences. Both \fIkey\fR and \fIvalue\fR 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.
\fIstring\fR is only iterated over once, so earlier key replacements
will have no affect for later key matches.  For example,
.RS
.PP
.CS
\fBstring map {abc 1 ab 2 a 3 1 0} 1abcaababcabababc\fR
.CE
.PP
will return the string \fB01321221\fR.
.PP
Note that if an earlier \fIkey\fR is a prefix of a later one, it will
completely mask the later one.  So if the previous example is
reordered like this,
.PP
.CS
\fBstring map {1 0 ab 2 a 3 abc 1} 1abcaababcabababc\fR
.CE
.PP
it will return the string \fB02c322c222c\fR.
.RE
.TP
\fBstring match\fR ?\fB\-nocase\fR? \fIpattern\fR \fIstring\fR
.
See if \fIpattern\fR matches \fIstring\fR; return 1 if it does, 0 if
it does not.  If \fB\-nocase\fR 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 \fIpattern\fR:
.RS
.IP \fB*\fR 10
Matches any sequence of characters in \fIstring\fR, including a null
string.
.IP \fB?\fR 10
Matches any single character in \fIstring\fR.
.IP \fB[\fIchars\fB]\fR 10
Matches any character in the set given by \fIchars\fR.  If a sequence
of the form \fIx\fB\-\fIy\fR appears in \fIchars\fR, then any
character between \fIx\fR and \fIy\fR, inclusive, will match.  When
used with \fB\-nocase\fR, the end points of the range are converted to
lower case first.  Whereas {[A\-z]} matches
.QW _
when matching case-sensitively (since
.QW _
falls between the
.QW Z
and
.QW a ),
with \fB\-nocase\fR this is considered like {[A\-Za\-z]} (and
probably what was meant in the first place).
.IP \fB\e\fIx\fR 10
Matches the single character \fIx\fR.  This provides a way of avoiding
the special interpretation of the characters \fB*?[]\e\fR in
\fIpattern\fR.
.RE
.TP
\fBstring range \fIstring first last\fR
.
Returns a range of consecutive characters from \fIstring\fR, starting
with the character whose index is \fIfirst\fR and ending with the
character whose index is \fIlast\fR. An index of 0 refers to the first
character of the string.  \fIfirst\fR and \fIlast\fR may be specified
as for the \fBindex\fR method.  If \fIfirst\fR is less than zero then
it is treated as if it were zero, and if \fIlast\fR is greater than or
equal to the length of the string then it is treated as if it were
\fBend\fR.  If \fIfirst\fR is greater than \fIlast\fR then an empty
string is returned.
.TP
\fBstring repeat \fIstring count\fR
.
Returns \fIstring\fR repeated \fIcount\fR number of times.
.TP
\fBstring replace \fIstring first last\fR ?\fInewstring\fR?
.
Removes a range of consecutive characters from \fIstring\fR, starting
with the character whose index is \fIfirst\fR and ending with the
character whose index is \fIlast\fR.  An index of 0 refers to the
first character of the string.  \fIFirst\fR and \fIlast\fR may be
specified as for the \fBindex\fR method.  If \fInewstring\fR is
specified, then it is placed in the removed character range.  If
\fIfirst\fR is less than zero then it is treated as if it were zero,
and if \fIlast\fR is greater than or equal to the length of the string
then it is treated as if it were \fBend\fR.  If \fIfirst\fR is greater
than \fIlast\fR or the length of the initial string, or \fIlast\fR is
less than 0, then the initial string is returned untouched.
.TP
\fBstring reverse \fIstring\fR
.
Returns a string that is the same length as \fIstring\fR but with its
characters in the reverse order.
.TP
\fBstring tolower \fIstring\fR ?\fIfirst\fR? ?\fIlast\fR?
.
Returns a value equal to \fIstring\fR except that all upper (or title)
case letters have been converted to lower case.  If \fIfirst\fR is
specified, it refers to the first char index in the string to start
modifying.  If \fIlast\fR is specified, it refers to the char index in
the string to stop at (inclusive).  \fIfirst\fR and \fIlast\fR may be
specified using the forms described in \fBSTRING INDICES\fR.
.TP
\fBstring totitle \fIstring\fR ?\fIfirst\fR? ?\fIlast\fR?
.
Returns a value equal to \fIstring\fR except that the first character
in \fIstring\fR 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 \fIfirst\fR is specified, it
refers to the first char index in the string to start modifying.  If
\fIlast\fR is specified, it refers to the char index in the string to
stop at (inclusive).  \fIfirst\fR and \fIlast\fR may be specified
using the forms described in \fBSTRING INDICES\fR.
.TP
\fBstring toupper \fIstring\fR ?\fIfirst\fR? ?\fIlast\fR?
.
Returns a value equal to \fIstring\fR except that all lower (or title)
case letters have been converted to upper case.  If \fIfirst\fR is
specified, it refers to the first char index in the string to start
modifying.  If \fIlast\fR is specified, it refers to the char index in
the string to stop at (inclusive).  \fIfirst\fR and \fIlast\fR may be
specified using the forms described in \fBSTRING INDICES\fR.
.TP
\fBstring trim \fIstring\fR ?\fIchars\fR?
.
Returns a value equal to \fIstring\fR except that any leading or
trailing characters present in the string given by \fIchars\fR are removed.  If
\fIchars\fR is not specified then white space is removed (any character
for which \fBstring is space\fR returns 1, and "\e0").
.TP
\fBstring trimleft \fIstring\fR ?\fIchars\fR?
.
Returns a value equal to \fIstring\fR except that any leading
characters present in the string given by \fIchars\fR are removed.  If
\fIchars\fR is not specified then white space is removed (any character
for which \fBstring is space\fR returns 1, and "\e0").
.TP
\fBstring trimright \fIstring\fR ?\fIchars\fR?
.
Returns a value equal to \fIstring\fR except that any trailing
characters present in the string given by \fIchars\fR are removed.  If
\fIchars\fR is not specified then white space is removed (any character
for which \fBstring is space\fR returns 1, and "\e0").
.SS "OBSOLETE SUBCOMMANDS"
.PP
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.
.TP
\fBstring bytelength \fIstring\fR
.
Returns a decimal string giving the number of bytes used to represent
\fIstring\fR in memory when encoded as Tcl's internal modified UTF\-8;
Tcl may use other encodings for \fIstring\fR as well, and does not
guarantee to only use a single encoding for a particular \fIstring\fR.
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.
.RS
.PP
In almost all cases, you should use the
\fBstring length\fR operation (including determining the length of a
Tcl byte array value).  Refer to the \fBTcl_NumUtfChars\fR manual
entry for more details on the UTF\-8 representation.
.PP
Formally, the \fBstring bytelength\fR operation returns the content of
the \fIlength\fR field of the \fBTcl_Obj\fR structure, after calling
\fBTcl_GetString\fR to ensure that the \fIbytes\fR 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.)
.PP
\fICompatibility note:\fR it is likely that this subcommand will be
withdrawn in a future version of Tcl. It is better to use the
\fBencoding convertto\fR command to convert a string to a known
encoding and then apply \fBstring length\fR to that.
.PP
.CS
\fBstring length\fR [encoding convertto utf-8 $theString]
.CE
.RE
.TP
\fBstring wordend \fIstring charIndex\fR
.
Returns the index of the character just after the last one in the word
containing character \fIcharIndex\fR of \fIstring\fR.  \fIcharIndex\fR
may be specified using the forms in \fBSTRING INDICES\fR.  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.
.TP
\fBstring wordstart \fIstring charIndex\fR
.
Returns the index of the first character in the word containing character
\fIcharIndex\fR of \fIstring\fR.  \fIcharIndex\fR may be specified using the
forms in \fBSTRING INDICES\fR.  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.
.SH "STRING INDICES"
.PP
When referring to indices into a string (e.g., for \fBstring index\fR
or \fBstring range\fR) the following formats are supported:
.IP \fIinteger\fR 10
For any index value that passes \fBstring is integer \-strict\fR,
the char specified at this integral index (e.g., \fB2\fR would refer to the
.QW c
in
.QW abcd ).
.IP \fBend\fR 10
The last char of the string (e.g., \fBend\fR would refer to the
.QW d
in
.QW abcd ).
.IP \fBend\-\fIN\fR 10
The last char of the string minus the specified integer offset \fIN\fR (e.g.,
.QW \fBend\-1\fR
would refer to the
.QW c
in
.QW abcd ).
.IP \fBend+\fIN\fR 10
The last char of the string plus the specified integer offset \fIN\fR (e.g.,
.QW \fBend+\-1\fR
would refer to the
.QW c
in
.QW abcd ).
.IP \fIM\fB+\fIN\fR 10
The char specified at the integral index that is the sum of
integer values \fIM\fR and \fIN\fR (e.g.,
.QW \fB1+1\fR
would refer to the
.QW c
in
.QW abcd ).
.IP \fIM\fB\-\fIN\fR 10
The char specified at the integral index that is the difference of
integer values \fIM\fR and \fIN\fR (e.g.,
.QW \fB2\-1\fR
would refer to the
.QW b
in
.QW abcd ).
.PP
In the specifications above, the integer value \fIM\fR contains no
trailing whitespace and the integer value \fIN\fR contains no
leading whitespace.
.SH EXAMPLE
.PP
Test if the string in the variable \fIstring\fR is a proper non-empty
prefix of the string \fBfoobar\fR.
.PP
.CS
set length [\fBstring length\fR $string]
if {$length == 0} {
    set isPrefix 0
} else {
    set isPrefix [\fBstring equal\fR \-length $length $string "foobar"]
}
.CE
.SH "SEE ALSO"
expr(n), list(n)
.SH KEYWORDS
case conversion, compare, index, match, pattern, string, word, equal,
ctype, character, reverse
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