One liners for File system disk usage.
 

Hi,

I am trying to develop a script 1 liner to check disk usage on file system, if it is more than 80% it should send email if it is less than than it should echo say "Do nothing"

However for both of them I am having some syntax problems:(:(

1)if [[ (df -P|egrep -i 'test'|awk '{print$5}'|sed 's/%//') >= 80 ]]; then mailx -s "test FULL" testme@testmail.com else echo "do nothing" fi

I am getting error message like.
-bash: conditional binary operator expected
-bash: expected `)'
-bash: syntax error near `|'

If I do with single square brackets.

2) if [ (df -P|egrep -i 'test' |awk '{print$5}'|sed 's/%//') >= 80 ]; then mailx -s "test is FULL" testme@testmail.com else echo "do nothing" fi
-bash: syntax error near unexpected token `df'

What the heck is difference between if with single and double square brackets Guru's?

Please assist in my understanding.

Many thanks.

Thanks for that Chris. I got a good understanding that [[ ]] are fairly strong than that of [ ] and that when it says conditional binary operator expected so I changed >= to -ge but still that error prevails...

Lastly I have now introduced " " and " " within if conditional statement but still no good and it just hangs...

Here we go this is code.

if [[ "(df -P|egrep -i 'test' |awk '{print$5}'|sed 's/%//')" -ge "80" ]]; then mailx -s "test" test@testmail.com else echo "do nothing" fi;

Personally when doing math comparisons I like to keep with the familiar operators, hence it is often just easier to use (()), eg.

grail mate:) you come up with some sensational command ! :):) need some time to digest, your stuff is working but I would love to understand where I am making mistake and where I do need to improve. weekend is going to be with shell scripting :):)

Have a close look between your df ... statement and mine (hint: look before df command)

That is my gross mistake, :( "$" sign is the answer :)

(( )) denotes an calculation
$( cmd ) substitutes the expression with the output of cmd. This is called a "parameter expansion"
( cmd; cmd2 | cmd3 ) just groups all comamnds avoiding a subshell
<( cmd ) executes cmd and connects stdout of cmd to a filedescriptor from which the calling script reads.

[someTest] is the portable POSIX way of testing. Available in nearly each and every shell.
[[ someTest ]] is the modern bash way. Has a lot more features and makes script easier to read.

Cooking !

Getting closer but still not that close :(

Now the one liner is working but still i am having issues using mailx

if [[ $(df -P|egrep -i '/test'|awk '{print$5}'|sed 's/%//') -ge 80 ]]; then mailx -s "test is FULL" email@removed </tmp/$$; else echo "do nothing"; fi

The above one liner remains in hang state unless and until I perform Ctl-C operation (twice).

How can get work around with it satisfying as it becomes truly one liner.

Say for example

echo "test is more than 80% FULL" > /tmp/$$;if [[ $(df -P|egrep -i '/test'|awk '{print$5}'|sed 's/%//') -ge 80 ]]; then mailx -s "test is FULL" email@removed </tmp/$$; else echo "do nothing"; fi

This works but it doesn't have charm of being a one liner.

But say if this comes the only one way then what should we do to.
1 echo statement reflects right value of %percentage used rather than just 80?