Bash variable assignment before command

Question

A couple of days ago I came across a command

AWS_ACCESS_KEY=\"foo\" AWS_SECRET_KEY=\"bar\" aws list iam

I see that setting variables before

Answer 1

Shell is substituting your variable before running the command inside $(). You can use && to make it work for you:

dname=$(date +%d_%m_%y) && mkdir ${dname} && cd ${dname}

or, of course:

dname=$(date +%d_%m_%y); mkdir ${dname} && cd ${dname}

However, dname would be available to mkdir if it were to grab the environment variable inside.

Let's say we have a script test.sh that has a single statement echo $dname inside. Then:

dname=$(date +%d_%m_%y) ./test.sh

would yield:

07_03_17

This is consistent with how your aws command line worked.

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Answer 2

you are missing && before mkdir below is complete statement you desire:

dname=$(date +%d_%m_%y) && mkdir ${dname} && cd ${dname}

Also if its not necessary to declare dname you can do: mkdir $(date +%d_%m_%y) && cd ${dname} both will give same answer