regexp(3tcl) Tcl Built-In Commands regexp(3tcl)
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NAME
regexp - Match a regular expression against a string
SYNOPSIS
regexp ?switches? exp string ?matchVar? ?subMatchVar subMatchVar ...?
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DESCRIPTION
Determines whether the regular expression exp matches part or all of
string and returns 1 if it does, 0 if it does not, unless -inline is
specified (see below). (Regular expression matching is described in
the re_syntax reference page.)
If additional arguments are specified after string then they are
treated as the names of variables in which to return information about
which part(s) of string matched exp. MatchVar will be set to the range
of string that matched all of exp. The first subMatchVar will contain
the characters in string that matched the leftmost parenthesized subex-
pression within exp, the next subMatchVar will contain the characters
that matched the next parenthesized subexpression to the right in exp,
and so on.
If the initial arguments to regexp start with - then they are treated
as switches. The following switches are currently supported:
-about Instead of attempting to match the regular expression,
returns a list containing information about the regular
expression. The first element of the list is a subex-
pression count. The second element is a list of prop-
erty names that describe various attributes of the regu-
lar expression. This switch is primarily intended for
debugging purposes.
-expanded Enables use of the expanded regular expression syntax
where whitespace and comments are ignored. This is the
same as specifying the (?x) embedded option (see the
re_syntax manual page).
-indices Changes what is stored in the matchVar and subMatchVars.
Instead of storing the matching characters from string,
each variable will contain a list of two decimal strings
giving the indices in string of the first and last char-
acters in the matching range of characters.
-line Enables newline-sensitive matching. By default, newline
is a completely ordinary character with no special mean-
ing. With this flag, “[^” bracket expressions and “.”
never match newline, “^” matches an empty string after
any newline in addition to its normal function, and “$”
matches an empty string before any newline in addition
to its normal function. This flag is equivalent to
specifying both -linestop and -lineanchor, or the (?n)
embedded option (see the re_syntax manual page).
-linestop Changes the behavior of “[^” bracket expressions and “.”
so that they stop at newlines. This is the same as
specifying the (?p) embedded option (see the re_syntax
manual page).
-lineanchor Changes the behavior of “^” and “$” (the “anchors”) so
they match the beginning and end of a line respectively.
This is the same as specifying the (?w) embedded option
(see the re_syntax manual page).
-nocase Causes upper-case characters in string to be treated as
lower case during the matching process.
-all Causes the regular expression to be matched as many
times as possible in the string, returning the total
number of matches found. If this is specified with
match variables, they will contain information for the
last match only.
-inline Causes the command to return, as a list, the data that
would otherwise be placed in match variables. When us-
ing -inline, match variables may not be specified. If
used with -all, the list will be concatenated at each
iteration, such that a flat list is always returned.
For each match iteration, the command will append the
overall match data, plus one element for each subexpres-
sion in the regular expression. Examples are:
regexp -inline -- {\w(\w)} " inlined "
→ in n
regexp -all -inline -- {\w(\w)} " inlined "
→ in n li i ne e
-start index Specifies a character index offset into the string to
start matching the regular expression at. The index
value is interpreted in the same manner as the index ar-
gument to string index. When using this switch, “^”
will not match the beginning of the line, and \A will
still match the start of the string at index. If -in-
dices is specified, the indices will be indexed starting
from the absolute beginning of the input string. index
will be constrained to the bounds of the input string.
-- Marks the end of switches. The argument following this
one will be treated as exp even if it starts with a -.
If there are more subMatchVars than parenthesized subexpressions within
exp, or if a particular subexpression in exp does not match the string
(e.g. because it was in a portion of the expression that was not
matched), then the corresponding subMatchVar will be set to “-1 -1” if
-indices has been specified or to an empty string otherwise.
EXAMPLES
Find the first occurrence of a word starting with foo in a string that
is not actually an instance of foobar, and get the letters following it
up to the end of the word into a variable:
regexp {\mfoo(?!bar\M)(\w*)} $string -> restOfWord
Note that the whole matched substring has been placed in the variable
“->”, which is a name chosen to look nice given that we are not actu-
ally interested in its contents.
Find the index of the word badger (in any case) within a string and
store that in the variable location:
regexp -indices {(?i)\mbadger\M} $string location
This could also be written as a basic regular expression (as opposed to
using the default syntax of advanced regular expressions) match by pre-
fixing the expression with a suitable flag:
regexp -indices {(?ib)\<badger\>} $string location
This counts the number of octal digits in a string:
regexp -all {[0-7]} $string
This lists all words (consisting of all sequences of non-whitespace
characters) in a string, and is useful as a more powerful version of
the split command:
regexp -all -inline {\S+} $string
SEE ALSO
re_syntax(3tcl), regsub(3tcl), string(3tcl)
KEYWORDS
match, parsing, pattern, regular expression, splitting, string
Tcl 8.3 regexp(3tcl)
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