Canon Camera, Hackers Manual

Page: 118 / 257

5.4 Lua primer
109
%s
String
%q Quoted string. The string is formatted so that it can safely be read back
by
Lua .
%% %. No argument expected.
i,j = string.find(s1, s2, k)
Searches for the substring
s2
in string
s1
and returns the indices for the first and the
last character of s2 . If s2 is not a substring of s1 , the function returns nil . The param-
eter
k
is optional and may specify the start index for the search.
t,n = string.gsub(s1,s2,s3,k)
Replaces all occurrences of string s2 in string s1 with string s3 . Returns the resulting
string and the replacement count. The optional parameter
k
can limit the number of
replacements.
The functions find() and gsub() accept patterns, too—strings with inter-
spersed control sequences. Most control sequences start with “%” followed
by a character, optionally followed by a modifier character (see below).
These control sequences describe character classes such as “letters” or
“digits”.
. All characters
%a Letters
%c Control characters such as new line or form feed
%d Digits
%l Lowercase letters
%p
Punctuation characters
%s
Whitespace characters
%u Uppercase letters
%w Alphanumeric characters
%x Hexadecimal digits
%z The character “0”
% Escape character. % followed by another character represents the
character itself. Escaping is particularly necessary for the characters
( ) . % + - * ? [ ^ $ . For example, “%%” represents “%”.
Using uppercase control characters after the “%” negates the character
class identified by the corresponding lowercase character. For example,
%S
stands for anything except white space.
You can define your own character sets by enclosing the characters be-
longing to the set within brackets:
[+–] for example, means ‘+’ or ‘–’.