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Accepted
Alistair Prestidge
Asked: 2013-05-01 02:20:22 +0800 CST

set -- $(cat /proc/loadavg)

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Hi I have a munin plugin that does this

load_fetch()  {
set -- $(cat /proc/loadavg)
cat <<EOF                                                                                                                                                                           
load1.value $1                                                                                                                                                                      
load5.value $2                                                                                                                                                                      
load15.value $3                                                                                                                                                                     
EOF                                                                                                                                                                                 
}

I was woundering if any one could tell me what the "set --" is doing? its not an east thing to google for and get results.

bash

2 Answers

  1. Best Answer

    http://www.gnu.org/software/bash/manual/html_node/The-Set-Builtin.html has an explanation. This command (re)sets the argument variables ($1, $2, $3, $4 and $5 in this case). cat /proc/loadavg gives you a line with some numbers, feeding the output to set -- maps those numbers to the $N-variables.

    See for instance:

    $ echo $1 $2

$ set -- HELLO WORLD
$ echo $1
HELLO
$ echo $2
WORLD
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  2. "Set --" is a bash clause and therefore not specific to munin. Getting to the bash help for the set parameter you can find this:

    -- If no arguments follow this option, then the positional parameters are unset. Otherwise, the positional parameters are set to the arguments, even if some of them begin with a `-'.

    In your specific case, what it does is map/pass on the contents of cat/proc/loadavg as parameters $1 $2 and $3 so afterwars they can assign them to load1.value, load5.value and load15.value respectively

    For further info use man or the following url: http://www.gnu.org/software/bash/manual/html_node/The-Set-Builtin.html

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