POSIX tools are great, but Julia code that relies on them will not be portable.
Also, spawning executables takes a lot of time, so for simple tasks it is often orders of magnitude faster to use Julia code than to spawn a POSIX command-line program.
For example, run(pipeline(`tail -n +2 $inputname`, stdout=outputname)) seems to be about 10²× slower on my computer than my native-Julia readuntil code above for most files.