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166 lines
4.7 KiB
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166 lines
4.7 KiB
Markdown
[#]: collector: (lujun9972)
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[#]: translator: (geekpi)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Generating numeric sequences with the Linux seq command)
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[#]: via: (https://www.networkworld.com/article/3511954/generating-numeric-sequences-with-the-linux-seq-command.html)
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[#]: author: (Sandra Henry-Stocker https://www.networkworld.com/author/Sandra-Henry_Stocker/)
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Generating numeric sequences with the Linux seq command
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======
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The Linux seq command can generate lists of numbers and at lightning speed. It's easy to use and flexible, too.
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[Jamie][1] [(CC BY 2.0)][2]
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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:
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```
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$ seq 5
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1
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2
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3
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4
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5
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```
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Unless directed otherwise, **seq** always starts with 1. You can start a sequence with a different number by inserting it before the final number.
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```
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$ seq 3 5
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3
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4
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5
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```
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### Specifying an increment
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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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[][3]
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```
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$ seq 3 3 18
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3
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6
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9
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12
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15
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18
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```
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You can elect to go from larger to smaller numbers by using a negative increment (i.e., a decrement).
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```
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$ seq 18 -3 3
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18
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15
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12
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9
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6
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3
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```
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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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Advertisement
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```
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$ time seq 1000000
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1
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2
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3
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…
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…
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999998
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999999
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1000000
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real 0m9.290s <== 9+ seconds
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user 0m0.020s
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sys 0m0.899s
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```
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## Using a separator
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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.
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```
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$ seq -s: 3 3 18
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3:6:9:12:15:18
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```
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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.
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**[ Also see [Invaluable tips and tricks for troubleshooting Linux][4]. ]**
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```
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$ seq -s' ' 3 3 18
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3 6 9 12 15 18
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```
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### Getting to the math
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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:
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```
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$ seq -s* 5 | bc
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120
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```
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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.
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```
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$ seq -s* 5
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1*2*3*4*5
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```
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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.
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```
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$ time seq -s* 117 | bc
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39699371608087208954019596294986306477904063601683223011297484643104\
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22041758630649341780708631240196854767624444057168110272995649603642\
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560353748940315749184568295424000000000000000000000000000
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real 0m0.003s
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user 0m0.004s
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sys 0m0.000s
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```
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### Limitations
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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:
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```
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$ echo {a..g}
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a b c d e f g
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```
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Join the Network World communities on [Facebook][5] and [LinkedIn][6] to comment on topics that are top of mind.
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--------------------------------------------------------------------------------
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via: https://www.networkworld.com/article/3511954/generating-numeric-sequences-with-the-linux-seq-command.html
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作者：[Sandra Henry-Stocker][a]
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选题：[lujun9972][b]
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译者：[译者ID](https://github.com/译者ID)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://www.networkworld.com/author/Sandra-Henry_Stocker/
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[b]: https://github.com/lujun9972
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[1]: https://creativecommons.org/licenses/by/2.0/
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[2]: https://creativecommons.org/licenses/by/2.0/legalcode
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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)
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[4]: https://www.networkworld.com/article/3242170/linux/invaluable-tips-and-tricks-for-troubleshooting-linux.html
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[5]: https://www.facebook.com/NetworkWorld/
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[6]: https://www.linkedin.com/company/network-world
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