Shell Programming and Scripting

chmod +x firstline
echo "original line" >testfile
cat testfile
./firstline "another line" testfile
cat testfile

bash-2.05$ cat firstline
#!/bin/sh

echo "$1" | cat - "$2" >$$
mv $$ "$2"
bash-2.05$ chmod +x firstline
bash-2.05$ echo "original line" >testfile
bash-2.05$ cat testfile
original line
bash-2.05$ ./firstline "another line" testfile
bash-2.05$ cat testfile
another line
original line
bash-2.05$