Mastering the Linux ‘seq’ Command: Quick Ways to Generate Number Lists

Basic Usage

One of the simplest ways to generate a list of numbers in Linux is with the seq command, which prints a sequence from 1 up to the given number.

$ seq 5
1
2
3
4
5

Custom Start and End

By providing a start and an end, you can begin the sequence at a number other than 1.

$ seq 3 5
3
4
5

Specifying Increment

You can define an increment (step) value. For example, to list multiples of 3 up to 18:

$ seq 3 3 18
3
6
9
12
15
18

A negative increment generates a descending sequence.

$ seq 18 -3 3
18
15
12
9
6
3

Performance

The seq command is very fast; generating one million numbers typically finishes in under ten seconds.

$ time seq 1000000
1
2
3
…
999998
999999
1000000

real    0m9.290s
user    0m0.020s
sys     0m0.899s

Using Separators

With the -s option you can replace the default newline separator with any character, such as a colon:

$ seq -s: 3 3 18
3:6:9:12:15:18

Using a space as the separator prints the sequence on a single line.

$ seq -s' ' 3 3 18
3 6 9 12 15 18

Feeding to bc for Calculations

By choosing a suitable separator, the output of seq can be piped directly into the arbitrary‑precision calculator bc. For example, multiplying numbers 1 through 5:

$ seq -s* 5 | bc
120

Even very large products can be computed quickly:

$ time seq -s* 117 | bc
39699371608087208954019596294986306477904063601683223011297484643104\
22041758630649341780708631240196854767624444057168110272995649603642\
560353748940315749184568295424000000000000000000000000000
real    0m0.003s
user    0m0.004s
sys     0m0.000s

Limitations

seq

accepts only a single separator, which can restrict more complex calculations. It also works exclusively with numbers; to generate an alphabetic sequence you should use brace expansion instead.

$ echo {a..g}
a b c d e f g