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Seq command

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Seq is a little known Linux command which is actually quite useful in while loops as it  can generate integer and floating point sequences with given increment. With -f parameter it can also insert them into arbitrary text strings.

By default seq sends to standard output a sequence of numbers.

seq [OPTION]... LAST
seq [OPTION]... FIRST LAST
seq [OPTION]... FIRST INCREMENT LAST  

Options

-f, --format=FORMAT
use printf style floating-point FORMAT (default: %g)
-s, --separator=STRING
use STRING to separate numbers (default: \n)
-w, --equal-width
equalize width by padding with leading zeroes
--help
display this help and exit
--version
output version information and exit

If FIRST or INCREMENT is omitted, it defaults to 1. That is, an omitted INCREMENT defaults to 1 even when LAST is smaller than FIRST. FIRST, INCREMENT, and LAST are interpreted as floating point values. INCREMENT is usually positive if FIRST is smaller than LAST, and INCREMENT is usually negative if FIRST is greater than LAST. When given, the FORMAT argument must contain exactly one of the printf-style, floating point output formats %e, %f, %g  


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[Dec 30, 2010] Seq command - revisited

September 12, 2006 | Wee Keat's Jumblog

I realised that I left out another crucial option for the seq command, that is the -f command. This is basically the formatting option, which allows you to format the results using the printf style floating-point FORMAT.

An example:

me@mycomp:~$
me@mycomp:~$ seq -f "line: %g" 1 5
line: 1
line: 2
line: 3
line: 4
line: 5

Now, with the option above, the practical side of it is now very obvious. Let's say I want to generate a pool of test email address… ahh… you see it too eh!

Here we go:

me@mycomp:~$
me@mycomp:~$ seq -f "email_%g@example.com" 1 5
email_1@example.com
email_2@example.com
email_3@example.com
email_4@example.com
email_5@example.com

Now, let's generate this email list and have them separated by comma.

me@mycomp:~$
me@mycomp:~$ seq -s ',' -f "email_%g@example.com" 1 5
me@mycomp:~$ mail_1@example.com,email_2@example.com,email_3@example.com,email_4@example.com,email_5@example.com

So… there you go, as promised, a nice and practical example of using the seq command. From now on, if you need a million sample emails in CSV format, just use the following:

me@mycomp:~$
me@mycomp:~$ seq -f "email_%g@example.com,firstname,lastname" 1 1000000 > emaillist.txt

You can also pipe them to other commands. Get creative!

Do you know about the obscure Linux command 'seq'????? It is actually quite cool.

Examples

seq 10
1
2
3
4
5
6
7
8
9
10
seq 3 9
3
4
5
6
7
8
9
seq 10 10 110
10
20
30
40
50
60
70
80
90
100
110

seq has c-style format capabilities. For example

seq -f "harvey%02g" 10

will produce a sequence of ten strings each starting with harvey and ending with a number:

harvey01
harvey02
harvey03
harvey04
harvey05
harvey06
harvey07
harvey08
harvey09
harvey10

To make these words into empty files, you use the "touch" comand. "touch" followed by a legal filename will update the timestamp of the file referred to. But, if there is no file of that name, touch creates it!

This can be used for generation of files like in the folllowing example:

touch $(seq -f "harvey%02g" 10)



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