r$, n = PatternReplaceStr(s$, pat$, repl[, n, encoding])
PatternReplaceStr()
can be used to modify a string's contents using pattern matching.
This function is powerful and can be used for all kinds of string operations. It returns
a copy of s$
in which all occurrences of the pattern pat$
have been replaced by a replacement
string specified by repl
. PatternReplaceStr()
also returns, as a second value, the total
number of substitutions made.
The third argument repl
can be either a string or a callback function. If repl
is a string,
then its value is used for replacement. Any sequence in repl
of the form %n
, with n
between
1 and 9, stands for the value of the n-th captured substring (see below). If repl
is a function,
then this function is called every time a match occurs, with all captured substrings passed
as arguments, in order; if the pattern specifies no captures, then the whole match is passed
as a sole argument. If the value returned by this function is a string, then it is used as the
replacement string; otherwise, the replacement string is the empty string.
The optional argument n
limits the maximum number of substitutions to occur. For instance,
when n
is 1 only the first occurrence of pat$
is replaced.
The pattern specified in pat$
is made up of a sequence of pattern items. A pattern item is usually
a character class which in turn represents a set of characters. The following combinations are allowed
in describing a character class:
x (where x is not one of the magic characters ^$()%.[]*+-?)
. (a dot)
%a
%c
%d
%g
%l
%p
%s
%u
%w
%x
%z
%x (where x is any non-alphanumeric character)
x
. This is the standard way to escape the magic characters. Any punctuation
character (even the non magic) can be preceded by a %
when used to represent itself in a pattern.
[set]
-
. All classes %x
described above may also be
used as components in set. All other characters in set represent themselves. For example, [%w_]
(or [_%w]
)
represents all alphanumeric characters plus the underscore, [0-7]
represents the octal digits, and
[0-7%l%-]
represents the octal digits plus the lowercase letters plus the -
character. The interaction
between ranges and classes is not defined. Therefore, patterns like [%a-z]
or [a-%%]
have no meaning.
[^set]
For all classes represented by single letters (%a
, %c
, etc.), the corresponding uppercase letter represents
the complement of the class. For instance, %S
represents all non-space characters.
The following items are valid pattern items:
*
, which matches 0 or more repetitions of characters
in the class. These repetition items will always match the longest possible sequence
+
, which matches 1 or more repetitions of characters in
the class. These repetition items will always match the longest possible sequence
-
, which also matches 0 or more repetitions of characters
in the class. Unlike *
, these repetition items will always match the shortest possible sequence
?
, which matches 0 or 1 occurrence of a character in the class
%n
, for n
between 1 and 9; such item matches a substring equal to the n-th captured string (see below)
%bxy
, where x
and y
are two distinct characters; such item matches strings that start with x
, end with y
,
and where the x
and y
are balanced. This means that, if one reads the string from left to right, counting +1 for
an x
and -1 for a y
, the ending y
is the first y
where the count reaches 0. For instance, the item %b()
matches
expressions with balanced parentheses.
A pattern is a sequence of pattern items. A ^
at the beginning of a pattern anchors the match at the beginning
of the subject string. A $
at the end of a pattern anchors the match at the end of the subject string. At
other positions, ^
and $
have no special meaning and represent themselves.
A pattern may contain sub-patterns enclosed in parentheses; they describe captures. When a match succeeds,
the substrings of the subject string that match captures are stored (captured) for future use. Captures are
numbered according to their left parentheses. For instance, in the pattern (a*(.)%w(%s*))
, the part of the
string matching a*(.)%w(%s*)
is stored as the first capture (and therefore has number 1); the character
matching .
is captured with number 2, and the part matching %s*
has number 3.
As a special case, the empty capture () captures the current string position (a number). For instance, if
we apply the pattern ()aa()
on the string "flaaap", there will be two captures: 3 and 5.
A pattern cannot contain embedded zeros. Use %z
instead.
The optional encoding
parameter can be used to set the character encoding
to use. This defaults to the default string encoding set using SetDefaultEncoding().
See Character encodings for details.
s$ = PatternReplaceStr("Hello World", "(%w+)", "%1 %1")The code above returns "Hello Hello World World"
s$ = PatternReplaceStr("Hello World from Hollywood", "(%w+)%s*(%w+)", "%2 %1")The code above returns "World Hello Hollywood from"
s$ = PatternReplaceStr("home = $HOME, user = $USER", "%$(%w+)", GetEnv)The code above returns "home = /home/andreas, user = andreas" (on Linux).
Local t = {name = "Hollywood", version="5.0"} s$ = PatternReplaceStr("$name_$version.jpg", "%$(%w+)", Function(v) Return(t[v]) EndFunction)The code above returns "Hollywood_5.0.jpg"