Can I get some help on this please, I have looked at the many post with similar questions and have tried the solutions and they are not working for my scenario which is:

I have a text file (myfile) that contains

b_log=$g_log/FILENAME.log
echo "Begin processing file FILENAME " >> $b_log

I have a script which contains a variable and tries to replace the string FILENAME in myfile with the value of var with the following commands:
var=/mydir/areally/really/really/deep/dir/structure/myfile.dat
perl -pi -e "s/FILENAME/\${var}/g" myfile

after I run the script the string FILENAME is removed but the value in var is not inserted.

try this
perl -pi -e "s/FILENAME/${var}/g" myfile

I tried that
var=$g_bin/MISSPIGGY/dc0000.auto_deploy.MISSPIGGY.PRD.cp_austin.20081007122846.26060
perl -pi -e "s/FILENAME/${var}/g" myfile

and am getting the following error:
Bareword found where operator expected at -e line 1, near "s/FILENAME//dbmgtu01"
syntax error at -e line 1, near "s/FILENAME//dbmgtu01"
Execution of -e aborted due to compilation errors.
Any ideals as to why it is not working?

oh ho...try using ":" insted of "/" in regex
that is

Thank you so much for your help, that was perfect.