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|Contents||Bulletin||Scripting in shell and Perl||Network troubleshooting||History||Humor|
|Examples of for loops||Examples of while loops||exec command||Usage of pipes with loops|
|Arithmetic expressions||Comparison operators||BASH Debugging||Shell history||Seq command||Humor||Etc|
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
- -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
- display this help and exit
- 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
Do you know about the obscure Linux command 'seq'????? It is actually quite cool.
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.
me@mycomp:~$ seq -f "line: %g" 1 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 "firstname.lastname@example.org" 1 5
Now, let's generate this email list and have them separated by comma.me@mycomp:~$
me@mycomp:~$ seq -s ',' -f "email@example.com" 1 5
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 "firstname.lastname@example.org,firstname,lastname" 1 1000000 > emaillist.txt
You can also pipe them to other commands. Get creative!
seq 10seq has c-style format capabilities. For example
seq 3 9
seq 10 10 110
seq -f "harvey%02g" 10
will produce a sequence of ten strings each starting with harvey and ending with a number:
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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