replace a particular text in all the files using single line shell command
this one is very simple, without for or loop, and takes care of any number or nested directories
grep -rl 'oldText' [folderName-optional] | xargs sed -i 's/oldText/newText/g'
There are probably less verbose solutions, but here we go:
for i in *; do sed -i 's/old/new/g' "$i"; done
Mind you, it will only work on the current level of the file system, files in subdirectories will not be modified. Also, you might want to replace * with *.php, or make backups (pass an argument after -i, and it will make a backup with the given extension).
sed -i.bak 's/old/new/g' *.php
to do it recursively
find /path -type f -iname '*.php' -exec sed -i.bak 's/old/new/' "{}" +;