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, ~ % 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+) end
   local i1,i2 = find(s,'%s*$')
   if i2 >= i1 then s = sub(s,,i1-) end
   return s
 end
 -- based on penlight 0.7.

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

 function trim10(s)
   local a = s:match('^%s*()')
   local b = s:match('()%s*$', a)
   return s:sub(a,b-)
 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' \t\n\v\f\r'
  local nospace =  - space
  local ptrim = space^ * lpeg.C((space^ * nospace^)^)
  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' \t\r\n\f\va\000b \r\t\n\f\v' == 'a\000b')
 end

 local function perftest(f, s)
   local time = os.clock  -- os.time or os.clock
   local t1 = time()
   for i=, 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=, 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