what is the method to find common lines in subset of multiple files in ubuntu

if there is at least two files have common lines hope to show like this example,

perl a.pl ./*.txt

common line1 - a.txt b.txt
common line2 - a.txt c.txt d.txt

i searched this script, but this script only search words, not common lines

perl theScript.pl ?.dat 
#! perl -nl

push @{ $h{ $_ } }, $ARGV

}{

print qq[$_ id in @{$h{ $_ }}] for keys %h;

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