用Lua实现string的trim()方法

function trim1(s)
  return (s:gsub("^%s*(.-)%s*$", "%1"))
end
-- from PiL2 20.4

function trim2(s)
  return s:match "^%s*(.-)%s*$"
end
-- variant of trim1 (match)

function trim3(s)
  return s:gsub("^%s+", ""):gsub("%s+$", "")
end
-- two gsub's

function trim4(s)
  return s:match"^%s*(.*)":match"(.-)%s*$"
end
-- variant of trim3 (match)

function trim5(s)
  return s:match'^%s*(.*%S)' or ''
end
-- warning: has bad performance when s:match'^%s*$' and #s is large

function trim6(s)
  return s:match'^()%s*$' and '' or s:match'^%s*(.*%S)'
end
-- fixes performance problem in trim5.
-- note: the '()' avoids the overhead of default string capture.
-- This overhead is small, ~ 10% for successful whitespace match call
-- alone, and may not be noticeable in the overall benchmarks here,
-- but there's little harm either.  Instead replacing the first `match`
-- with a `find` has a similar effect, but that requires localizing
-- two functions in the trim7 variant below.

local match = string.match
function trim7(s)
  return match(s,'^()%s*$') and '' or match(s,'^%s*(.*%S)')
end
-- variant of trim6 (localize functions)

local find = string.find
local sub = string.sub
function trim8(s)
  local i1,i2 = find(s,'^%s*')
  if i2 >= i1 then s = sub(s,i2+1) end
  local i1,i2 = find(s,'%s*$')
  if i2 >= i1 then s = sub(s,1,i1-1) end
  return s
end
-- based on penlight 0.7.2

function trim9(s)
  local _,i1 = find(s,'^%s*')
  local i2 = find(s,'%s*$')
  return sub(s,i1+1,i2-1)
end
-- simplification of trim8

function trim10(s)
  local a = s:match('^%s*()')
  local b = s:match('()%s*$', a)
  return s:sub(a,b-1)
end
-- variant of trim9 (match)

function trim11(s)
 local n = s:find"%S"
 return n and s:match(".*%S", n) or ""
end
-- variant of trim6 (use n position)
-- http://lua-users.org/lists/lua-l/2009-12/msg00904.html

function trim12(s)
 local from = s:match"^%s*()"
 return from > #s and "" or s:match(".*%S", from)
end
-- variant of trim11 (performs better for all
-- whitespace string). See Roberto's comments
-- on ^%s*$" v.s. "%S" performance:
-- http://lua-users.org/lists/lua-l/2009-12/msg00921.html

do
 require 'lpeg'
 local space = lpeg.S' 	
vf
'
 local nospace = 1 - space
 local ptrim = space^0 * lpeg.C((space^0 * nospace^1)^0)
 local match = lpeg.match
 function trim13(s)
   return match(ptrim, s)
 end
end
-- lpeg.  based on http://lua-users.org/lists/lua-l/2009-12/msg00921.html

do
 require 'lpeg'
 require 're'
 local ptrim = re.compile"%s* {(%s* %S+)*}"
 local match = lpeg.match
 function trim14(s)
   return match(ptrim, s)
 end
end
-- variant with re module.

require 'trim'
local trim15 = trim
-- C implementation (see separate trim.c file)


-- test utilities

local function trimtest(trim)
  assert(trim'' == '')
  assert(trim' ' == '')
  assert(trim'  ' == '')
  assert(trim'a' == 'a')
  assert(trim' a' == 'a')
  assert(trim'a ' == 'a')
  assert(trim' a ' == 'a')
  assert(trim'  a  ' == 'a')
  assert(trim'  ab cd  ' == 'ab cd')
  assert(trim' 	
fva00b 
	
fv' == 'a00b')
end

local function perftest(f, s)
  local time = os.clock  -- os.time or os.clock
  local t1 = time()
  for i=1,100000 do
    f(s)f(s)f(s)f(s)f(s)f(s)f(s)f(s)f(s)f(s)
  end
  local dt = time() - t1
  io.stdout:write(string.format("%4.1f",dt) .. ' ')
end

local trims = {trim1, trim2, trim3, trim4, trim5, trim6, trim7,
               trim8, trim9, trim10, trim11, trim12, trim13, trim14, trim15}

-- correctness tests
for _,trim in ipairs(trims) do
  trimtest(trim)
end

-- performance tests
for j=1,3 do
  for i,trim in ipairs(trims) do
    io.stdout:write(string.format("%2d",i) .. ": ")
    perftest(trim,  "")
    perftest(trim,  "abcdef")
    perftest(trim,  "   abcdef   ")
    perftest(trim,  "abcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdefabcdef")
    perftest(trim,  "  a b c d e f g h i j k l m n o p q r s t u v w x y z A B C ")
    perftest(trim,  "                               a                            ")
    perftest(trim,  "                                                            ")
    print()
  end
end

原文地址：http://lua-users.org/wiki/StringTrim