How to insert an incremented line count?

[Josef Lowder]

How can one insert an incremented line count number 
at the beginning of every line of a text file? 

A shell script that I had on my old unix system used to do 
something like this, but I can't get it to work on my current 
linux system. 

# increment - increments line-sequence numbers 

grep -v "=" $1 ^
grep -n '^' ^
sed 's/^\([1-9]\):\(.*\)/000\1:\2/
s/^\([1-9][0-9]\):\(.*\)/00\1:\2/
s/^\([1-9][0-9][0-9]\):\(.*\)/0\1:\2/
s/^\([0-9][0-9][0-9][0-9]\):\(.*\)\.\([0-9][0-9][0-9][0-9]\)\(.*\)/\2\.\1\4/'