diff --git a/command_prompt.py b/command_prompt.py
index 0801d62..99f28f0 100644
--- a/command_prompt.py
+++ b/command_prompt.py
@@ -4,6 +4,8 @@ from kivy.graphics import Color,Rectangle
 import glob
 import os.path
 
+import filecheck
+
 class Command_prompt(Label):
     
     def __init__(self,app,**kwargs):
@@ -309,35 +311,13 @@ class Command_prompt(Label):
                     self.message="error: no file is open for editing, specify a path"
                     return
 
-            # check that the file is not a directory
-            if os.path.isdir(self.argv[1]):
-                self.message="error: '"+self.argv[1]+"' is a directory"
+            (ret,self.message)=filecheck.check_write(self.argv[1],self.argv[0]=="w!")
+            # add comment if no overwrite
+            if ret==-2:
+                self.message+=" (use ':w!' to overwrite)"
+            if ret<0:
                 return
-            # check that file does not already exist
-            if self.argv[0]!="w!" and self.argv[1]!= self.app.openfile and os.path.isfile(self.argv[1]):
-                self.message="error: '"+self.argv[1]+"' already exists (use ':w!' to overwrite)"
-                return
-            # check that the containing directory exists
-            if len(os.path.dirname(self.argv[1]))>0 and not os.path.isdir(os.path.dirname(self.argv[1])):
-                self.message="error: could not find directory '"+os.path.dirname(self.argv[1])+"'"
-                return
-            # check permissions
-            if os.path.isfile(self.argv[1]):
-                if not os.access(self.argv[1],os.W_OK):
-                    self.message="error: permission denied: cannot write to file '"+self.argv[1]+"'"
-                    return
-            else:
-                # check write to directory
-                if len(os.path.dirname(self.argv[1]))>0:
-                    if not os.access(os.path.dirname(self.argv[1]),os.W_OK):
-                        self.message="error: permission denied: cannot write to parent directory '"+os.path.dirname(self.argv[1])+"'"
-                        return
-                else:
-                    if not os.access(os.getcwd(),os.W_OK):
-                        self.message="error: permission denied: cannot write to parent directory '"+os.getcwd()+"'"
-                        return
 
-            # if we haven't returned yet
             self.app.openfile=self.argv[1]
             self.app.readonly=False
             self.app.painter.write(self.argv[1])
@@ -353,36 +333,23 @@ class Command_prompt(Label):
                 self.message="error: could not open file: no argument found -- usage: ':e <path to file>'"
                 return
 
-            # check that the file is not a directory
-            if os.path.isdir(self.argv[1]):
-                self.message="error: '"+self.argv[1]+"' is a directory"
+            # check that the file can be edited
+            (ret,self.message)=filecheck.check_edit(self.argv[1])
+            # error
+            if ret<0:
                 return
+
             if os.path.isfile(self.argv[1]):
-                # check permissions
-                if not os.access(self.argv[1],os.R_OK):
-                    self.message="error: permission denied: cannot read file '"+self.argv[1]+"'"
-                    return
                 # read the file
                 self.app.painter.read(self.argv[1])
                 # set readonly mode
                 self.app.readonly=not os.access(self.argv[1],os.W_OK)
-
             else:
-                # check write to directory
-                if len(os.path.dirname(self.argv[1]))>0:
-                    if not os.access(os.path.dirname(self.argv[1]),os.W_OK):
-                        self.message="error: permission denied: cannot write to parent directory '"+os.path.dirname(self.argv[1])+"'"
-                        return
-                else:
-                    if not os.access(os.getcwd(),os.W_OK):
-                        self.message="error: permission denied: cannot write to parent directory '"+os.getcwd()+"'"
-                        return
                 # new file, reset painter
                 self.app.painter.reset()
                 self.app.readonly=False
 
-            # if we haven't returned yet
-            # select openfile
+            # select openfile in app
             self.app.openfile=self.argv[1]
             # update status bar
             self.app.status_bar.draw()
diff --git a/filecheck.py b/filecheck.py
new file mode 100644
index 0000000..36631b1
--- /dev/null
+++ b/filecheck.py
@@ -0,0 +1,46 @@
+import os.path
+
+# check that a file can be edited
+def check_edit(file):
+    # check that the file is not a directory
+    if os.path.isdir(file):
+        return(-1,"error: '"+file+"' is a directory")
+    if os.path.isfile(file):
+        # check permissions
+        if not os.access(file,os.R_OK):
+            return(-2,"error: permission denied: cannot read file '"+file+"'")
+    else:
+        # check write to directory
+        if len(os.path.dirname(file))>0:
+            if not os.access(os.path.dirname(file),os.W_OK):
+                return(-3,"error: permission denied: cannot write to parent directory '"+os.path.dirname(file)+"'")
+        else:
+            if not os.access(os.getcwd(),os.W_OK):
+                return(-4,"error: permission denied: cannot write to parent directory '"+os.getcwd()+"'")
+    return(0,"")
+
+
+# check that a file can be written
+def check_write(file,overwrite):
+    # check that the file is not a directory
+    if os.path.isdir(file):
+        return(-1,"error: '"+file+"' is a directory")
+    # check that file does not already exist
+    if not overwrite and os.path.isfile(file):
+        return(-2,"error: '"+file+"' already exists")
+    # check that the containing directory exists
+    if len(os.path.dirname(file))>0 and not os.path.isdir(os.path.dirname(file)):
+        return(-3,"error: could not find directory '"+os.path.dirname(file)+"'")
+    # check permissions
+    if os.path.isfile(file):
+        if not os.access(file,os.W_OK):
+            return(-4,"error: permission denied: cannot write to file '"+file+"'")
+    else:
+        # check write to directory
+        if len(os.path.dirname(file))>0:
+            if not os.access(os.path.dirname(file),os.W_OK):
+                return(-5,"error: permission denied: cannot write to parent directory '"+os.path.dirname(file)+"'")
+        else:
+            if not os.access(os.getcwd(),os.W_OK):
+                return(-6,"error: permission denied: cannot write to parent directory '"+os.getcwd()+"'")
+    return(0,"")