file1.js

var exec = require('child_process').exec;

	function wew(){
		exec("iwlist wlan2 scan|grep -Po '(?<=Address: )\\S+|(?<=Signal level=)\\S+|(?<=ESSID:\")[^\"]+'", test);
	}
	
	function test(error, stdout, stderr) { 
		var out = stdout.replace(/^\s+/mg, '');
		out = out.split('\n');
		var cells = [];
		var line;
		var info = {};
	 
		for (var i=0,l=out.length-1,m=1; i<l; i++,m++) {
			line = out[i];
			if(i%3 == 0 && i!=0){
				cells.push(info);
				info = {};
			}
			 
			if(m%3==1)		{ 	info['mac'] = line; 	}
			else if(m%3==2)	{ 	info['signal'] = line; 	}
			else if(m%3==0)	{	info['essid'] = line; 	}
		}
		cells.push(info);
		// console.log(cells);
		for (var i in cells) {
		//  console.log("the array: " + cells[i].mac); //"aa", bb", "cc"
		}
		
		
		return cells;
		
	}
		
exports.command = wew;

main.js

var reader = require( './file1.js' );
var bang = reader.command();
console.log(bang);

file1.js, line 32: Return to where? exec calls it -- and ignores the return value. You need to pass the value forward, in a callback to your original code.