Create directories with incrementing variables as part of directory name using Bash within for loop

Question

I am trying to write a bash script which allows me to automate the creation of multiple directories with incrementing names.

For example, I am trying to create the directories named v0v1, v1v2, ... , v40v41.

I have tried using a 'for' loop, where I create a variable and set this to be equal to the current value of i+1 (where 'i' is the current loop iteration), but it is not working as expected. I have managed to get the variable to increment (and have checked this using 'echo'), but I cannot get it to become part of the new directory name.

The code I have written is as follows:

for i in {0..40}; do let r=$((i+1)); mkdir v$iv$r; done

However, the directories produced have names only containing the first variable value (i.e. v0, v1, ..., v40), and do not include the 'v$r' at all.

Does anyone have any ideas how to use two variables at once in the same filename?

mikeserv · Accepted Answer · 2014-03-27 12:12:14Z

1

printf 'r=%d ; mkdir v$((r-1))v${r} ;' $(seq 2 41) |sh

You don't need a shell loop at all.

answered Mar 27, 2014 at 12:12

mikeserv

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John1024 · Accepted Answer · 2014-03-27 04:16:36Z

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for i in {0..40}; do let r=$((i+1)); mkdir v${i}v$r; done

When bash sees the expression v$iv$r, it substitutes in for variables iv and r. But, of course, there is no iv. So bash substitutes in the empty string. The solution is to use braces to assure that bash knows where the variable name ends. Thus: v${i}v$r.

answered Mar 27, 2014 at 4:16

John1024

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1 Comment

jthill Over a year ago

For something this simple I'd skip the separate r and just for i in {0..40}; do mkdir v${i}v$((i+1)); done

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