How to split a bash command?

Question

I have the following command

mkdir -p /tmp/{A,B,C,D}

The above command working fine, but not the below as bash considering B,C and D as different commands:

I want something like below:

mkdir -p /tmp/{A,
B,
C,
D}

It looks as if this answer solve your problem. http://stackoverflow.com/a/7316194/1606556 — MarcelHodan, Feb 01 '16 at 12:17
If your script is run by `sh`, you cannot use `bash` constructs. In a script run by `bash`, the linked answer should work. This is unrelated to the linked answer, but probably relevant for this question. — tripleee, Feb 01 '16 at 12:19
I am running using sh and ./script-name. Ut is creating {A, folder under /tmp and B, and C} under PWD. — Balasekhar Nelli, Feb 01 '16 at 12:22
So, again, slowly: Don't use `sh` if you want to use `bash` constructs. Use `bash` if you want to use `bash` constructs. — tripleee, Feb 01 '16 at 12:23
Even with bash, it is creating {A, folder under /tmp and B, and C} under PWD. — Balasekhar Nelli, Feb 01 '16 at 12:27
That's because whitespace is not ignored. Remove all whitespace and you should get what you expect. — tripleee, Feb 01 '16 at 12:27

tripleee · Answer 1 · 2016-02-01T12:30:21.510

As noted in comments, you can do this with backslashes before the newlines, but any whitespace will be regarded as significant, and the whole thing will end up rather ugly. As an aesthetically more pleasurable workaround, you can put the directory names in an array.

dirs=(
    a
    b
    c
    d
  )
mkdir -p "${dirs[@]/#//tmp/}"

The construct "${array[@]/#/prefix)" reproduces the values in array with the prefix prefix added before each.

This is relatively obscure, though; unless the real directory names you are creating are very long and cumbersome, simply writing them out in longhand would be my recommendation.

As noted in comments, both arrays and {A,B,C,D} are Bash constructs, so will not be available if you invoke sh instead of bash (even when sh is a symlink to bash; Bash will notice, and enable POSIX mode).

Thanks tripleee. You saved my day. In fact the of the directories are very cumbersome. Using array will make it easy. — Balasekhar Nelli, Feb 01 '16 at 12:36
Accept and/or upvote are the recommended ways to say thanks here. Nudge & wink. — tripleee, Feb 01 '16 at 12:38

How to split a bash command?

1 Answers1