Lua Programming/stringlib

Facilities

string.len

Usage

string.len(STRING)

Description

The string.len function returns the length of the string argument.

print (string.len("Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch"))  -- Returns 58

Embedded nul characters

Embedded nul characters do not terminate the string and are also counted by this function.

print (string.len("ab\000cd\000"))  -- Returns 6

The length operator can also be used to determine the length of a string

The lua programming language provides a length operator, which can also be used to determine the length of a string:

print (#"Llanfairpwllgwyngyllgogerychwyrndrobwllllantysiliogogogoch")  -- Returns 58

string.reverse

Usage

string.reverse(STRING)

Description

The string.reverse function can be used for reversing string and returns the string with its character order reversed:

print (string.reverse("anut fo raj a rof tun A"))  -- A nut for a jar of tuna

string.sub

Usage

string.sub(STRING, STARTPOS [, ENDPOS])

Description

The string.sub function returns a substring of the string argument from a start position, and an optional end position.

print (string.sub("cheese salad sandwich",8))  -- position 8 onwards gives us "salad sandwich"
print (string.sub("cheese salad sandwich",1,12)  -- positions 1 to 12 gives us "cheese salad"

The start position cannot be omitted, but the end position may be omitted

Note that the start position is not optional, so for substrings starting at the first position, a parameter of one must be provided:

-- This does not work
print (string.sub("cheese salad sandwich",,12)  -- we cannot omit the start position
-- To fix this, we must provide a substring position
print (string.sub("cheese salad sandwich",1,12)  -- we want a substring from position 1

The end position can be omitted or negative

Without an end position, the substring continues to the end of the string:

print (string.sub("cheese salad sandwich",8))  -- position 8 onwards gives us "salad sandwich"

String positions may be negative

The end position can be negative. A negative value indicates the number of characters from the end, with -1 meaning the last character, -2 meaning the last but one character, etc:

print (string.sub("cheese salad sandwich",-8))  -- start 8 characters from the end gives "sandwich"
print (string.sub("cheese salad sandwich",1,-9))  -- drop " sandwich" to give "cheese salad"