If you're in a Unix-type system, you may find that the file utility is much easier than grepping files for strings, especially strings like "print" that aren't that unique to a particular type of file. For instance:

$ file aa.php
aa.php: PHP script text
$ file test.pl
test.pl: a perl script text executable
$ file hello.c
hello.c: ASCII C program text
$ file package.sh
package.sh: POSIX shell script text executable
[download]