Curly Brace Group in Linux BASH

In Linux BASH shell, you can use curly brace {} to represent a set of possible values in an array. For example,

1	touch abc{1,2,3,4}

touch abc{1,2,3,4}

This will be equivalent to four command as follows and as a result, 4 files will be generated.

touch abc1
touch abc2
touch abc3
touch abc4

touch abc1
touch abc2
touch abc3
touch abc4

Please note that there should not be spaces inside the curly braces. For example,

1 2	~$ echo abc{1, 2, 3, 4} abc{1, 2, 3, 4}

~$ echo abc{1, 2, 3, 4}
abc{1, 2, 3, 4}

However,

1 2	~$ echo abc{" 1"," 2"," 3"," 4"} abc 1 abc 2 abc 3 abc 4

~$ echo abc{" 1"," 2"," 3"," 4"}
abc 1 abc 2 abc 3 abc 4

This is useful, if you want to make several folders under a specific directory, you can use this elegant solution:

1	mkdir /some/dir/{a,b,c,d}

mkdir /some/dir/{a,b,c,d}

This will create four commands as:

mkdir /some/dir/a
mkdir /some/dir/b
mkdir /some/dir/c
mkdir /some/dir/d

mkdir /some/dir/a
mkdir /some/dir/b
mkdir /some/dir/c
mkdir /some/dir/d

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