Using variables in a sed command

[pjb]

I am having problems using variables in a sed command.
For example, if I want to convert all ocurrances of AAA to BBB in file1 resulting if file2, I can use

sed 's/AAA/BBB/g' file1 > file2

If I try it with variables like this, it doesn't work

FROM="AAA"
TO="BBB"
sed 's/$FROM/$TO/g' file1 > file2

 

[StevetheBlue]

try using double-quotes instead of single.

Steve.

 

[Guest_imported]

I'm not sure why though. My UNIX book even shows examples of a similar sed with single quotes.

Thanks

 

[StevetheBlue]

Double-quotes allow the variables to be interpreted by the shell.

Steve.