readded udpated scripts directory

scripts/ow_v2.sh

@@ -0,0 +1,33 @@
+#!/bin/sh
+
+# overwrite: copy standard input to output after EOF
+# version 2. BUG here too
+
+PATH=/bin:/usr/bin
+
+case $# in
+1)      ;;
+*)      echo 'Usage: overwrite file' 1>&2; exit 2
+esac
+
+new=/tmp/overwr1.$$
+old=/tmp/overwr2.$$
+trap 'rm -f $new $old; exit 1' 1 2 15
+
+cat >$new       # collect the input
+cp $1 $old      # save original file
+
+trap '' 1 2 15  # we are committed; ignore signals
+cp $new $1
+
+rm -f $new $old
+
+# solving the original problem we had in ow_v1.sh:
+# If a DEL happens berfore the original file is touched, then the temporary files
+# are removed and the file is left alone. After the backup is made, signals are ignored
+# so the last cp won't be interrupted -- once the cp starts, overwrite is commited to
+# changing the original file.
+
+# However, this implementation is still flawed (see pg 154 of The Unix Programming Environment).
+
+# If the program providing input to overwrite gets an error, its output will be empty and overwrite will dutifully and reliably destroy the argument file. (see ow.sh for final version)