What's Linux test -a command test for?

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http://stackoverflow.com – Please take a look at the following code, snap=snapshot.file touch snapshot.file-1 $ [ -a $snap-1 ] && echo yes yes What does the test -a command tests for here? I tried info coreutils 'test invocation' and searched for -a, but didn't find it in the file characteristic tests section, but rather in the connectives for test section. Is such test -a command an undocumented one? (HowTos)