shell scripting : seq prints a sequence of numbers

Filed Under (bash) by Amandine on 08-02-2010

I often need to execute a loop x times, and I’m just too lazy to write a i++ style algorithm… the command seq is made for me :)

Easy to use, just does what I need from it, here’s a extract from the man page :

NAME
       seq - print a sequence of numbers

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

So…

$ seq 10
1
2
3
4
5
6
7
8
9
10
$ seq 5 10
5
6
7
8
9
10
$ seq 10 2 20
10
12
14
16
18
20
$ for i in `seq 5`; do echo 'hello!'; done;
hello!
hello!
hello!
hello!
hello!

Great ! :p

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Xargs

Filed Under (bash) by Amandine on 23-09-2009

Today I learnt a new command :D

$ xargs

Ok I’m a little bit lying : I knew it before but I was using it only to put several lines into one unique line, like this :

$ ls |xargs

Now, thanks to the new guy in front of me (the colorblind one), I will be able to replace a lot of “for” and ` ` by xargs :D

Some interesting uses of xargs :

$ ls | xargs -n 8

Display the content af the current directory in 8 colums

$ find /path -type f -print0 | xargs -0 rm

Seems to be more efficient than “find /path -exec rm {} \;”, because xargs splits this list into sublists and calls rm once for every sublist, while find calls rm once for every single file.

$ xargs -i ssh {} uptime < ./server.list

to get uptime of each server in server.list

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