Why does this command pipe prints nothing on Debian or Mac?

Question

This command prints the milliseconds till g.co ten times per second:

ping -i 0.1 g.co | grep ms

If I add just another grep it no longer prints anything ever (both on Mac and on Debian):

ping -i 0.1 g.co | grep ms | grep m

Why is that?

yes | grep y | grep y

This does print an infinite series of y lines as expected

Try `grep --line-buffered ...` – Mark Setchell Jun 29 '20 at 20:18 — Mark Setchell, Jun 29 '20 at 20:18

score 0 · Accepted Answer · answered Jun 30 '20 at 05:57

Just wait for some time. mac os waits for the buffer to fill up before printing the whole block.

If you do want immediate line-by-line output, you can add the "--line-buffered" flags to both grep commands, effectively making your command -

ping -i 0.1 g.co | grep ms --line-buffered | grep m --line-buffered

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