Bash – grep multiple file types recursively

You are attempting to edit in place (-i option) the STDIN.

Remove -i option, it is useless.

Note:

You can speed up the command a lot avoiding the second grep, excluding at the root the unnecessary directories

Try

grep -lIR --exclude-dir=.svn "dlclose" . | xargs sed -i bak 's/.*dlclose.*/\/\/&/g'  

or

for f in $(grep -lIR --exclude-dir=.svn "dlclose" .)
do
   sed -i bak 's/.*dlclose.*/\/\/&/g' $f
done

This would be my approach:

find dev -type f -print0 | \          # find all files
xargs -0 grep 'extends MY_Output' | \ # search for your string
cut -d/ -f2  | \                      # extract web folder name
sort | uniq                           # eliminate duplicates

Note use of the print0 parameter to find and the -0 (zero) flag to xargs, which prevents problems if your filenames have embedded spaces in them.