$ cat *.log
bar1
bar2
bar3
baz1
baz2
baz3
foo1
foo2
foo3

$ perl -ne 'print "$ARGV: $_"' *.log
bar.log: bar1
bar.log: bar2
bar.log: bar3
baz.log: baz1
baz.log: baz2
baz.log: baz3
foo.log: foo1
foo.log: foo2
foo.log: foo3

$ cat *.log | perl -ne 'print "$ARGV: $_"'
-: bar1
-: bar2
-: bar3
-: baz1
-: baz2
-: baz3
-: foo1
-: foo2
-: foo3

$ perl -i -ne 'print ucfirst $_' *.log
$ cat *.log
Bar1
Bar2
Bar3
Baz1
Baz2
Baz3
Foo1
Foo2
Foo3