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I have an alias in my server's /etc/profile which generates a random directory on command, like this: 

alias rdir="mkdir -p ./`cat /dev/random | tr -cd 'a-z0-9' | head -c 8`/"

But it turns out this generates always the same string (in this case: directory). I figured out already this seems to be related to source'ing the profile file and only generates a new random string after I call source /etc/profile.

Now, I wonder, how do I generate a random string in an alias which always changes when I call the alias, like in this example: rdir? (Without re-source-ing?)

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  • 2
    You also want to use /dev/urandom instead of /dev/random. Commented Jul 21, 2015 at 8:17
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    Why not simply use mktemp --tmpdir=. -d XXXXXXXX ? It would even check against existing folders an make sure it is a new directory. Commented Jul 21, 2015 at 8:51

2 Answers 2

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Use single quotes instead of double quotes:

alias rdir='mkdir -p ./$(cat /dev/urandom | tr -cd 'a-z0-9' | head -c 8)/'

Now, the statement is evaluated every time the alias is called. With double quotes the statement is evaluated, when defining the alias, therefore static.

Also a simpler solution to create a random directory inside the current working directory would be to use mktemp:

alias rdir='mktemp -d --tmpdir=./'
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You can also use pwgen instead of cating and filtering /dev/random:

alias mkranddir='mkdir $(pwgen -s 8 1)'
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  • pwgen is rarely installed on a default system. Commented Jun 20, 2022 at 10:29

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