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Overcome Bash's expansion order

Terminal - Overcome Bash's expansion order
eval "mkdir test{$(seq -s, 1 10)}"
2011-07-23 17:09:01
User: xakon
Functions: eval
Overcome Bash's expansion order

In order to create, let's say, 10 directories with a single process we can use the command:

mkdir test{1,2,3,4,5,6,7,8,9,10}

something extremely boring to type! Why not use seq?

seq -s, 1 10

and use its output inside the curly braces?

The obvious solution

mkdir test{$(seq -s, 1 10)}

is, unfortunately, too naive and doesn't work. The answer is the order of the shell expansions (feature of Bourne Shell, actually), where brace expansion happens before command substitution (according to Bash's manual).

The solution is to put another level of substitution, using the powerful and mystic command eval.

I found the trick in a similar problem in the post at http://stackoverflow.com/questions/6549037/bash-brace-expansion-in-scripts-not-working-due-to-unwanted-escaping


There are 2 alternatives - vote for the best!

Terminal - Alternatives
mkdir ${1..10}
2011-07-23 19:20:35
User: linuts
Functions: mkdir
Tags: bash

no need for seq or eval

Know a better way?

If you can do better, submit your command here.

What others think

lol, what bash versions you use?

mkdir test{1..10} works fine
Comment by zolden 192 weeks and 3 days ago

I'm sorry that didn't clarify enough my point, but I DON'T want to type these numbers in the command line. For example, I could use shell parameters or get another output from a program, which produces for example words and not numbers.

But, yes, of course, what you've written works perfectly fine on most recent versions of Bash! It's the hard-wired numbers that are unwanted here...

Comment by xakon 192 weeks and 3 days ago

Sorry, I didn't get it. You used "1" and "10", I used the same 2 numbers, not whole sequence. What's the difference?

Comment by zolden 192 weeks and 3 days ago

Ok, say you need something like this:

seq -s, 1 4 1000

How, are you going to write it?

Or, let's say you're creating the directories "lonely", "closely", "finally" and all these names are stored in a shell variable, or can be extracted from another program.

The numbers here are just an example. A simple, and maybe not very suitable, example. They don't really have any special meaning.

Comment by xakon 192 weeks and 3 days ago

>you need something like this:

>seq -s, 1 4 1000

The answer is

echo {1..100..4},
Comment by zolden 192 weeks and 3 days ago

Your point of view

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