perl -pie 's/old/new/g' ./*/*

##</code><code>##

perl -pie 's/old/new/g' subdir/file1 subdir/file2 subdir2/file1 subdir2/subsubdir/

##</code><code>##

perl -pi -e 's/old/new/g' file1 dir1/file2 /usr/local/file3 /tmp/*

##</code><code>##


perl -pie 's/old/new/g' ./*
perl -pie 's/old/new/g' ./*/*
perl -pie 's/old/new/g' ./*/*/*
perl -pie 's/old/new/g' ./*/*/*/*
perl -pie 's/old/new/g' ./*/*/*/*/*
etc.....