Generating numeric sequences with the Linux seq command
======
The Linux seq command can generate lists of numbers and at lightning speed. It's easy to use and flexible, too.
[Jamie][1] [(CC BY 2.0)][2]
One of the easiest ways to generate a list of numbers in Linux is to use the **seq** (sequence) command. In its simplest form, **seq** will take a single number and then list all the numbers from 1 to that number. For example:
```
$ seq 5
1
2
3
4
5
```
Unless directed otherwise, **seq** always starts with 1. You can start a sequence with a different number by inserting it before the final number.
```
$ seq 3 5
3
4
5
```
### Specifying an increment
You can also specify an increment. Say you want to list multiples of 3. Specify your starting point (first 3 in this example), increment (second 3) and end point (18).
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```
$ seq 3 3 18
3
6
9
12
15
18
```
You can elect to go from larger to smaller numbers by using a negative increment (i.e., a decrement).
```
$ seq 18 -3 3
18
15
12
9
6
3
```
The **seq** command is also very fast. You can probably generate a list of a million numbers in under 10 seconds.
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```
$ time seq 1000000
1
2
3
…
…
999998
999999
1000000
real 0m9.290s <== 9+ seconds
user 0m0.020s
sys 0m0.899s
```
## Using a separator
Another very useful option is to use a separator. Instead of listing a single number on each line, you can insert commas, colons or some other characters. The -s option followed by the character you wish to use.
```
$ seq -s: 3 3 18
3:6:9:12:15:18
```
In fact, if you simply want your numbers to be listed on a single line, you can use a blank as your separator in place of the default linefeed.
**[ Also see [Invaluable tips and tricks for troubleshooting Linux][4]. ]**
```
$ seq -s' ' 3 3 18
3 6 9 12 15 18
```
### Getting to the math
It may seem like a big leap to go from generating a sequence of numbers to doing math, but given the right separators, **seq** can easily prepare calculations that you can pass to **bc**. For example:
```
$ seq -s* 5 | bc
120
```
What is going on in this command? Let’s take a look. First, **seq** is generating a list of numbers and using * as the separator.
```
$ seq -s* 5
1*2*3*4*5
```
It’s then passing the string to the calculator (**bc**) which promptly multiplies the numbers. And you can do a fairly extensive calculation in a fraction of a second.
You only get to choose one separator, so your calculations will be very limited. Use **bc** by itself for more complicated math. In addition, **seq** only works with numbers. To generate a sequence of single letters, use a command like this instead:
```
$ echo {a..g}
a b c d e f g
```
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[3]: https://www.networkworld.com/article/3440100/take-the-intelligent-route-with-consumption-based-storage.html?utm_source=IDG&utm_medium=promotions&utm_campaign=HPE21620&utm_content=sidebar ( Take the Intelligent Route with Consumption-Based Storage)
