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(By default, prefer `grep &>/dev/null`) `grep -q` may exit as soon as it finds a match; this is a good optimization for when the input is a file. However, if the input is the output of another program, then that other program will receive SIGPIPE, and further writes will fail. When this happens, it might (bsdtar does) print a message about a "write error" to stderr. Which is going to confuse and alarm the user. In one of the cases (in common.bash, in the test suite), this had already been mitigated by wrapping bsdtar in "echo "$(bsdtar ...)", as Bash builtin echo doesn't complain if it gets SIGPIPE. However, that means we're storing the entire output of bsdtar in memory, which is silly. Additionally, the way it was implemented is also wrong; because it was being used with `grep -qv` instead of just `grep -q`, it *always* found a non-matching line (even something inconsequential like `%NAME%`), and *never* triggered a test failure. Looking at a few of these cases, it might also make sense to switch to using `bsdtar tf` instead of `bsdtar xf` when checking membership, but that's work for another day.
