API strfind

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Returns a pair of numbers representing the start and end of the first occurrence of the pattern within the string, if it exists.

startPos, endPos = string.find(string, pattern [, initpos [, plain]])
startPos, endPos = strfind(string, pattern [, initpos [, plain]])

Arguments

string

string - The string to examine.

pattern

string - The pattern to search for within string. This pattern is similar to Unix regular expressions, but is not the same -- see Lua Pattern matching for more details.

initpos

number - Index of the character within string to begin searching. As is usual for Lua string functions, 1 refers to the first character of the string, 2 to the second, etc. -1 refers to the last character of the string, -2 to the second last, etc. If this argument is omitted, it defaults to 1; i.e., the search begins at the beginning of string.

plain

boolean - Whether or not to disable regular expression matching. Defaults to false, so regex matching is usually enabled.

Returns

startPos

number - The position of the first character of the first occurrence of the pattern.

endPos

number - The position of the last character of the first occurrence of the pattern.

Example

Find the first occurrence of the pattern in the string passed. If an instance of the pattern is found a pair of values representing the start and end of the string is returned. If the pattern cannot be found nil is returned.

> = string.find("Hello Lua user", "Lua")
7       9
> = string.find("Hello Lua user", "banana")
nil

We can optionally specify where to start the search with a third argument. The argument may also be negative which means we count back from the end of the string and start the search.

> = string.find("Hello Lua user", "Lua", 1)  -- start at first character
7       9
> = string.find("Hello Lua user", "Lua", 8)  -- "Lua" not found again after character 8
nil
> = string.find("Hello Lua user", "e", -5)   -- first "e" 5 characters from the end
13      13

The pattern argument can be a regular expression which allows more complex searches. See the Patterns Tutorial on Lua-Users.org and Pattern matching for more information. We can turn off the regular expression feature by using the optional fourth argument plain. plain takes a boolean value and must be preceded by init. E.g.,

> = string.find("Hello Lua user", "%su")          -- find a space character followed by "u"
10      11
> = string.find("Hello Lua user", "%su", 1, true) -- turn on plain searches, now not found
nil

Sometimes it's more appropriate to use string.find, rather than string.gmatch, eg:

local msg = "Phase2:- There isn't any need for iterating over this mini-string.";
local startPos, endPos, firstWord, restOfString = string.find( msg, "(%w+)[%s%p]*(.*)");

Result:

startPos = 1
endPos = 66
firstWord = "Phase2"
restOfString = "There isn't any need for iterating over this mini-string."