Mfcttrf

I occasionally need to work with console commands and 100% of the time I want to redirect my output to a file I fail to redirect stderr as well as stdout the first time. I can't think of a single reason one would want the output and the error to got to different locations, especially since in most early programs what constituted error output and standard output was left entirely up to the programmer, and it's usage was wildly inconsistent.

I realize of course, I'm ranting in 2019. We've moved well past simply outputting to the console in most all respects; so much so it's very much the exception rather than the norm. In the early days of computing there might have been a good reason to separate stdout and stderr.

What, if it existed, was it?

Because you might not want error messages in your output. According to computer scientist Stephen C. Johnson:

One of the most amusing and unexpected consequences of
phototypesetting was the Unix standard error file (!). After
phototypesetting, you had to take a long wide strip of paper and feed
it carefully into a smelly, icky machine which eventually (several
minutes later) spat out the paper with the printing visible.

One afternoon several of us had the same experience -- typesetting
something, feeding the paper through the developer, only to find a
single, beautifully typeset line: "cannot open file foobar" The
grumbles were loud enough and in the presence of the right people, and
a couple of days later the standard error file was born...

You are thinking that all output is for human reading.

For instance, take the Unix cpio command. It writes the archive to stdout, which is always redirected to a device or file. It writes the archive with a header before each file that contains the size of the file, which lets it calculate the offset to the next file when reading it back.

If there was an error or warning thrown in there, it would basically make it unusable after that point due to the extra data thrown in the output. Plus you would want that warning to go to your screen or error log separately from the archive, otherwise you would never see it.