Testing for write permission is done by rc write redirection (echo >.tmp). If it fails then commands intended for such condition will not be executed. Use touch(1) for that test instead.

Reference: /n/sources/patch/patchapply-write-perm
Date: Wed Mar  4 02:29:10 CET 2015
Signed-off-by: antox@ml.lv

--- /rc/bin/patch/apply	Wed Mar  4 02:26:01 2015
+++ /rc/bin/patch/apply	Wed Mar  4 02:25:58 2015
@@ -23,7 +23,7 @@
 	exit badpatch
 }
 
-if(! echo >.tmp || ! rm .tmp){
+if(! touch .tmp || ! rm .tmp){
 	echo no write permission >[1=2]
 	exit 'no write permission'
 }