Sometimes it’s necessary to do things with sequences in Bash. If you want to create a bunch of directories that will be mount points for NFS servers you could do this:

# mkdir /mnt/fs42
# mkdir /mnt/fs42/vol0
# mkdir /mnt/fs42/vol1
# mkdir /mnt/fs42/vol2
# mkdir /mnt/fs42/vol3

But, even the best experts at the “up arrow key” wouldn’t want to do this for 50 file servers. A nested for loop would work, but it’s not necessarily the easiest way to go. The command seq makes a sequence of integers bounded by the numbers specified.

ok:

for i in `seq 1 50`; do for j in `seq 0 3`; do mkdir -p /mnt/fs$i/vol$j; done; done;

Using Bash sequences, you can tell the shell to interpret this {1..50} as a list of integers between 1 and 50. This also works with letters like {a..t}.

# echo {a..t}
a b c d e f g h i j k l m n o p q r s t
# echo {0..50}
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

way better:

# mkdir -p /mnt/fs{1..50}/vol{0..3}

of course if you have non-sequential lists, you may have to specify each element like this:

{1,3,4,5,6,9}