perf: use the IO each_line in the earlier stage of the process

spec/exec_spec.cr

@@ -37,6 +37,11 @@ describe Exec do
     Exec.each_line("ls spec").should eq ["exec_spec.cr\n", "spec_helper.cr\n"]
   end
 
+  it "ensure $? was set" do
+    Exec.each_line("unamea")
+    $?.exit_code.should eq 127
+  end
+
   it "list file with option" do
     Exec.each_line("ls spec", chomp: true).should eq ["exec_spec.cr", "spec_helper.cr"]
   end

src/exec.cr

@@ -28,12 +28,12 @@ class Exec < Process
 
   def self.each_line(command, chomp = false, &block : String ->) : Nil
     process = new(command, shell: true, input: Redirect::Inherit, output: Redirect::Pipe, error: Redirect::Inherit)
-    output = process.output.gets_to_end
-    status = process.wait
-    $? = status
-    output.each_line(chomp) do |line|
+    process.output.each_line(chomp) do |line|
       yield line
     end
+  ensure
+    status = process.wait
+    $? = status
   end
 
   def self.each_line(command, chomp = false)