This behaviour is easy to observe with the following command line: $ rm -f daao.*; strace -ff -o daao dash -c 'set -x; z=`echo | cut -f1 | sort`'
and then $ grep write daao.* daao.6716:write(2, "+ ", 2) = 2 daao.6716:write(2, "z=", 2) = 2 daao.6716:write(2, "\n", 1) = 1 daao.6718:write(2, "+ ", 2) = 2 daao.6718:write(2, "echo", 4) = 4 daao.6718:write(2, "\n", 1) = 1 daao.6718:write(1, "\n", 1) = 1 daao.6719:write(2, "+ ", 2) = 2 daao.6719:write(2, "cut", 3) = 3 daao.6719:write(2, " -f1", 4) = 4 daao.6719:write(2, "\n", 1) = 1 daao.6719:write(1, "\n", 1) = 1 daao.6720:write(2, "+ ", 2) = 2 daao.6720:write(2, "sort", 4) = 4 daao.6720:write(2, "\n", 1) = 1 daao.6720:write(1, "\n", 1) = 1 The subshells in pipeline prints their own commands before executing it, using multiple syscalls giving possibility of intermixed output when context switches happen in between... For comparison this is what bash gives: zao.6858:write(2, "+ z=\n", 5) = 5 zao.6860:write(2, "++ echo\n", 8) = 8 zao.6860:write(1, "\n", 1) = 1 zao.6861:write(2, "++ cut -f1\n", 11) = 11 zao.6861:write(1, "\n", 1) = 1 zao.6862:write(2, "++ sort\n", 8) = 8 zao.6862:write(1, "\n", 1) = 1 An alternative to concatenate strings to a buffer before writing one could try using gather write with writev() (I don't know the SMOP factor there as I did not peek the dash source code :) Tomi -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
