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Do you know about the obscure Linux command 'seq'????? It is actually quite cool.
seq 'prints' (sends to standard output) a sequence of numbers. By itself it does nothing, but with a few parameters it functions nicely.
Watch:
greg@workstation:~$ seq 10
1
2
3
4
5
6
7
8
9
10
greg@workstation:~$ seq 3 9
3
4
5
6
7
8
9
greg@workstation:~$ seq 10 10 110
10
20
30
40
50
60
70
80
90
100
110
greg@workstation:~$
But why would you want to do this?
To sequentially number files that don't exist yet using touch, for example!
seq has c-like format capabilities. For those of you who don't know c, this means that seq understands certain wildcard like tokens that are used to format stuff.
Let's say we want a sequence of files called "harvey" numbered from 01 to 10. The format for that would be %02g which can be put in the middle of a double-quoted string. So the string "harvey%02g" is a template. The command:
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!
So the string of made-up filenames is fed to touch as follows:
touch $(seq -f "harvey%02g" 10)
This one-liner will get you ten harveys!
Oh, the -f flag in seq tells seq to use the formatting codes.
Comments
So, it's like the jot command?
Posted by: Alcari | September 19, 2009 7:01 PM
I forgot all about seq; I last used it in 2003 to generate several GB of mock data files while testing an instrument which I was building at the time.
Posted by: MadScientist | September 19, 2009 9:32 PM
And danged handy combined with for
Posted by: D. C. Sessions | September 19, 2009 10:07 PM
The seq command has lots of power, but if you are using the bash shell, the last example can be done more simply as:
touch harvey{01..10}
Posted by: Ted Powell | September 20, 2009 1:04 AM
but harvey does not like to be touched that way
Posted by: harvey | September 20, 2009 8:19 AM