tar(1) was the command that often bit back at me across the different Un*x implementations, vs awk(1) which for some unknown reason I had internalized the most miniscule differences.

I got into the habit of immediately installing gtar on any Solaris box I had root on (damn the leading "/" in the archive).

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The 2nd worst part was dealing with SunOS and HP/UX at work and Ultrix outside of work. Worst part was not grokking why MS-DOS wouldn't buffer keystrokes the few times I was exposed to it.