bash - cat not working a pipe -

revised version of question:

cat - | tr "a-z" "a-z" | tr "a-z" "a-z" 

does not give output when run on bash shell prompt. have press ctrl-d o/p.

o/p

$ cat - | tr "a-z" "a-z" | tr "a-z" "a-z" test 

however works fine , output without using ctrl-d..why ?

cat - | tr "a-z" "a-z"  

o/p

$ cat - | tr "a-z" "a-z"  test test 

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original version of question:

cat "$@" | tr "a-z" "a-z" | tr "a-z" "a-z" 

hangs when run on bash shell prompt. why that?

my $@ empty.

however works this

cat "$@" | tr "a-z" "a-z"  

what you're seeing due buffering. in

cat - | tr a-z a-z | tr a-z a-z 

(no quotes needed) may not output after hit enter, because middle or third tr may have buffered data internally. @ point, flush buffers , you'll full, correct output. hitting ctrl-d closes pipe , forces flush.

this typical phenomenon when connecting several commands in 1 pipe.

by way, in this case (but not when using "$@"), cat - superfluous.