How to remove spaces from a string in Lua?

Question

I want to remove all spaces from a string in Lua. This is what I have tried:

string.gsub(str, "", "") string.gsub(str, "% ", "") string.gsub(str, "%s*", "") 

This does not seem to work. How can I remove all of the spaces?

Answer 1

It works, you just have to assign the actual result/return value. Use one of the following variations:

str = str:gsub("%s+", "") str = string.gsub(str, "%s+", "") 

I use %s+ as there's no point in replacing an empty match (i.e. there's no space). This just doesn't make any sense, so I look for at least one space character (using the + quantifier).

Answer 2

The fastest way is to use trim.so compiled from trim.c:

/* trim.c - based on http://lua-users.org/lists/lua-l/2009-12/msg00951.html             from Sean Conner */ #include <stddef.h> #include <ctype.h> #include <lua.h> #include <lauxlib.h>  int trim(lua_State *L) {  const char *front;  const char *end;  size_t      size;   front = luaL_checklstring(L,1,&size);  end   = &front[size - 1];   for ( ; size && isspace(*front) ; size-- , front++)    ;  for ( ; size && isspace(*end) ; size-- , end--)    ;   lua_pushlstring(L,front,(size_t)(end - front) + 1);  return 1; }  int luaopen_trim(lua_State *L) {  lua_register(L,"trim",trim);  return 0; } 

compile something like:

gcc -shared -fpic -O -I/usr/local/include/luajit-2.1 trim.c -o trim.so 

More detailed (with comparison to the other methods): http://lua-users.org/wiki/StringTrim

Usage:

local trim15 = require("trim")--at begin of the file local tr = trim("   a z z z z z    ")--anywhere at code