grep -Hn '<TAB>' *

##</code><code>##

cat -nT /tmp/foo | grep '\^I'

##</code><code>##

perl -lne 'print "$ARGV:$.:$_" if /\t/; close ARGV if eof' *

##</code><code>##

perl -ne 'print "$ARGV:$.:$_" if /\t/' /tmp/foo

##</code><code>##

for f in * ; do perl -ne 'print "$ARGV:$.:$_" if /\t/' $f; done