* Purify all corepkgs builders.

corepkgs/channels/unpack.sh.in

@@ -1,9 +1,7 @@
 #! @shell@ -e
 
-export PATH=/bin:/usr/bin # !!! impure
-
-mkdir $out
-mkdir $out/tmp
+@coreutils@/mkdir $out
+@coreutils@/mkdir $out/tmp
 cd $out/tmp
 
 expr=$out/default.nix
@@ -12,8 +10,8 @@ echo '[' > $expr
 nr=0
 for i in $inputs; do
     echo "unpacking $i"
-    @bunzip2@ < $i | tar xvf -
-    mv * ../$nr # !!! hacky
+    @bunzip2@ < $i | @tar@ xvf -
+    @coreutils@/mv * ../$nr # !!! hacky
     echo "(import ./$nr)" >> $expr
     nr=$(($nr + 1))
 done
@@ -21,4 +19,4 @@ done
 echo ']' >> $expr
 
 cd ..
-rmdir tmp
+@coreutils@/rmdir tmp

corepkgs/fetchurl/builder.sh.in

@@ -1,13 +1,11 @@
 #! @shell@ -e
 
-export PATH=/bin:/usr/bin
-
 echo "downloading $url into $out"
 
 prefetch=@storedir@/nix-prefetch-url-$outputHash
 if test -f "$prefetch"; then
     echo "using prefetched $prefetch";
-    mv $prefetch $out
+    @coreutils@/mv $prefetch $out
 else
     @curl@ --fail --location --max-redirs 20 "$url" > "$out"
 fi

corepkgs/nar/nar.sh.in

@@ -1,10 +1,7 @@
 #! @shell@ -e
 
-# !!! impure; fix this
-export PATH=/bin:/usr/bin
-
 echo "packing $path into $out..."
-mkdir $out
+@coreutils@/mkdir $out
 dst=$out/tmp.nar.bz2
 @bindir@/nix-store --dump "$path" > tmp
 
@@ -14,4 +11,4 @@ dst=$out/tmp.nar.bz2
 
 @bindir@/nix-hash --flat --type $hashAlgo --base32 $dst > $out/narbz2-hash
 
-mv $out/tmp.nar.bz2 $out/$(cat $out/narbz2-hash).nar.bz2
+@coreutils@/mv $out/tmp.nar.bz2 $out/$(@coreutils@/cat $out/narbz2-hash).nar.bz2