Shell Programming and Scripting

 if [ $isnext = n -o $isnext = N ]; then
	cat /tmp/input0.$$ >> $filename

$$: Expands to the process ID of the shell.  In a () subshell, it expands  to  the process ID of the current shell, not the subshell.

$ echo "Hello World!" > /tmp/myfile.$$
$ ls -l /tmp/myfile*
-rw-rw-r--. 1 rbatte1 users 48 Jul 22 14:15 /tmp/myfile.22384

#!/bin/bash

tmpdir=$(mktemp -d) || exit 1                        # Abort script if we cannot do this!
if [ -z "$DEBUG" ]
then
   trap "rm -rf $tmpdir" EXIT
else
   printf "Debug mode\n"
fi

echo "Hello world!" > $workdir/output.file

tmpdir=/tmp/tmp.dir.$$
mkdir -m 700 $tmpdir || exit 1                        # Abort script if we cannot do this!
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