CODEWITHSUNDEEP
bashbrace-expansion
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Reputation: 1767

Brace expansion with a Bash variable - {0..$foo}

WEEKS_TO_SAVE=4
mkdir -p weekly.{0..$WEEKS_TO_SAVE}

gives me a folder called weekly.{0..4}

Is there a secret to curly brace expansion while creating folders I'm missing?

Upvotes: 16

Views: 6674

Answers (5)

kev
kev

Reputation: 161734

bash does brace expansion before variable expansion, so you get weekly.{0..4}.
Because the result is predictable and safe (don't trust user input), you can use eval in your case:

$ WEEKS_TO_SAVE=4
$ eval "mkdir -p weekly.{0..$((WEEKS_TO_SAVE))}"

note:

  1. eval is evil
  2. use eval carefully

Here, $((..)) is used to force the variable to be evaluated as an integer expression.

Upvotes: 13

anubhava
anubhava

Reputation: 785276

Curly braces don't support variables in BASH, you can do this:

 for (( c=0; c<=WEEKS_TO_SAVE; c++ ))
 do
    mkdir -p weekly.${c}
 done

Upvotes: 12

jfg956
jfg956

Reputation: 16750

Another way of doing it without eval and calling mkdir only once:

WEEKS_TO_SAVE=4
mkdir -p $(seq -f "weekly.%.0f" 0 $WEEKS_TO_SAVE)

Upvotes: 11

SiegeX
SiegeX

Reputation: 140377

If you happen to have zsh installed on your box, your code as written will work with Z-shell if you use #!/bin/zsh as your interpreter:

Example

$ WEEKS_TO_SAVE=4
$ echo {0..$WEEKS_TO_SAVE}
0 1 2 3 4

Upvotes: 2

amit_g
amit_g

Reputation: 31250

Brace expansion does not support it. You will have to do it using a loop.

Brace expansion is performed before any other expansions, and any characters special to other expansions are preserved in the result. It is strictly textual. Bash does not apply any syntactic interpretation to the context of the expansion or the text between the braces. To avoid conflicts with parameter expansion, the string ‘${’ is not considered eligible for brace expansion

.

Upvotes: 2

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