ljunior-helper has already pointed out some of the issues with your last post. Let me expand on that a little bit.

No. A sed substitute command will replace the text you tell it to match with the text you tell it to substitute. It will only replace all instances of al if you tell it to replace all instances of al.

If you don't want it to replace all instances of al, describe more precisely what you want to match and what text you want to use to replace the matched text.

Your latest sample input file contains four instances of al and one instance of al2h6. One of those instances of al is at the start of a line and is followed by six spaces. One instance of al2h6 is at the start of a line and is followed by 3 spaces.

Can you precisely define what you want to match and what text you want to replace the text you match?

From your last request, I would guess that you don't want to replace al or al2h6, but instead want to replace eight characters at the start of a line starting with al with the eight replacement characters LONG0003. If that is what you want, that would be something more like:

Code:

sed 's/^al....../LONG0003/' file

Please stop making us guess at what you want and give precise details about what you are trying to do.