Append a text to the end of multiple files in Linux

You don't specify the shell, you could try the foreach command. Under tcsh (and I'm sure a very similar version is available for bash) you can say something like interactively:

foreach i (*.php)
foreach> echo "my text" >> $i
foreach> end

$i will take on the name of each file each time through the loop.

As always, when doing operations on a large number of files, it's probably a good idea to test them in a small directory with sample files to make sure it works as expected.

Oops .. bash in error message (I'll tag your question with it). The equivalent loop would be

for i in *.php
do 
   echo "my text" >> $i
done

If you want to cover multiple directories below the one where you are you can specify

*/*.php

rather than *.php

I usually use tee because I think it looks a little cleaner and it generally fits on one line.

echo "my text" | tee -a *.php