I have just found a couple of examples using [ -a some_dir ] or [ -a some_file ] but can't find what the -a operator is for. It seems it should be described in the man page for test/[ but there it is just as a comparison operator [ $expr1 -a $expr2 ]. It seems it simply returns true if a file or dir exists, no matter the type or so.
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In bash and some other shells, -a is a synonym for -e (true if file exists).
$ help test
...
-a FILE True if file exists.
...
-e FILE True if file exists.
This is non-standard and not supported in all shells, so you better don't rely on it.
Notice that the manpage of test(1) documents the external command (/usr/bin/test, /usr/bin/[, etc), not the shell built-in.
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and
helpis a shell builtin command that provides help on shell builtin commands. – X Tian Aug 6 at 9:17 -
2@XTian
helpis a bash built-in command which provides incomplete help on built-in commands ;-) – mosvy Aug 6 at 9:23 -
I was not aware of the difference between command and builtin. It is too often pointed out
testand[are the same command residing in/usr/bin. So, what is used whilst I am really testing with[? :)) – Honza Hejzl Aug 6 at 10:02 -
1You're always using the shell built-in no matter if you call it as
[ortest(unless you disabled it with egenable -n [). – mosvy Aug 6 at 10:16 -
btw, the external
test/[from GNU coreutils (the/usr/bin/testin "desktop" linux) used to support the unary-a. It no longer does – mosvy Aug 6 at 10:20
