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+[#]: collector: (lujun9972)
+[#]: translator: ( )
+[#]: reviewer: ( )
+[#]: publisher: ( )
+[#]: url: ( )
+[#]: subject: (Generating numeric sequences with the Linux seq command)
+[#]: via: (https://www.networkworld.com/article/3511954/generating-numeric-sequences-with-the-linux-seq-command.html)
+[#]: author: (Sandra Henry-Stocker https://www.networkworld.com/author/Sandra-Henry_Stocker/)
+
+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).
+
+[][3]
+
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+
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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.
+
+Advertisement
+
+```
+$ 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.
+
+```
+$ time seq -s* 117 | bc
+39699371608087208954019596294986306477904063601683223011297484643104\
+22041758630649341780708631240196854767624444057168110272995649603642\
+560353748940315749184568295424000000000000000000000000000
+
+real    0m0.003s
+user    0m0.004s
+sys     0m0.000s
+```
+
+### Limitations
+
+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
+```
+
+Join the Network World communities on [Facebook][5] and [LinkedIn][6] to comment on topics that are top of mind.
+
+--------------------------------------------------------------------------------
+
+via: https://www.networkworld.com/article/3511954/generating-numeric-sequences-with-the-linux-seq-command.html
+
+作者：[Sandra Henry-Stocker][a]
+选题：[lujun9972][b]
+译者：[译者ID](https://github.com/译者ID)
+校对：[校对者ID](https://github.com/校对者ID)
+
+本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
+
+[a]: https://www.networkworld.com/author/Sandra-Henry_Stocker/
+[b]: https://github.com/lujun9972
+[1]: https://creativecommons.org/licenses/by/2.0/
+[2]: https://creativecommons.org/licenses/by/2.0/legalcode
+[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)
+[4]: https://www.networkworld.com/article/3242170/linux/invaluable-tips-and-tricks-for-troubleshooting-linux.html
+[5]: https://www.facebook.com/NetworkWorld/
+[6]: https://www.linkedin.com/company/network-world