Bash error: missing [: missing `]'

Question

I an writing simple script in Bash, to check Linux file system disk usage on root file system and display a warning message if system is greater than 6%.

The commands are running in a terminal, however when I tried the if statement, I am getting this error on line 16 [: missing]'`

  1 #!/bin/bash
  2 
  3
  4  
  5 clear
  6 #checking for usage on the system and saving in a file usage1
  7 df -h / >usage1
  8
  9 #display current use to the screen
 10 clear
 11 echo
 12 awk '$5>6' usage1
 13
 14 #Creating variable to use in the awk if statemant
 15 usage2= "awk '{print $5}'/home/peters/usage1 | tail -n1 |cut -c1"
 16 #Building statemant
 17 if ($usage2>6)
 18 print "Warning file system greater than 6% !!"
 19
 20 exit 0

Answer 1

Your line 17 should be:

if [ $usage2 -gt 6 ]

You need to put a space after [ and before ]. Also, when comparing numbers, you should be using -eq, -ne, -gt, -lt, -ge, and -le rather than the familiar symbols.

Answer 2

You want (without any spaces around the =)

usage2=$(awk '{print $5}' /home/peters/usage1 | tail -n1 |cut -c1)

to put into the usage2 variable the output of your awk...|cut -c1 command. You need a space between the awk braced command and its input file name (but no spaces around =). BTW, you could simply use cut(1) as cut -f5 (instead of awk '{print $5}'...) to get the 5^th field.

BTW, you don't need any usage1, you could probably just code

usage2=$(df | cut -f5| tail -n1 | cut -c2)

^{But I did not test that.}

Then you should use

if [ "$usage2" -gt 6 ] ; then
   echo "Warning file system greater than 6% !!" > /dev/stderr
fi

to test(1) - it is often a shell builtin - and deal with empty variables value. Since it is an error message it should go to stderr, not stdout. And you don't want to use printf but echo (because printf(1) deals with % specially). Perhaps you want logger(1) ...

But your approach (asking here, perhaps twice) is brittle (and asking twice is rude!). You need to learn more about shells. Read the advanced bash scripting guide, you won't loose your time. Also, use a good editor for writing your shell script. Some editors (emacs) have quite good modes for shells - with syntax coloring that helps! ...

BTW, starting temporarily your script with #!/bin/bash -vx would help during the debugging phase. And remove the clear commands, you don't want them...

At last, did you consider using disk quotas?

Answer 3

Try writing your if statement like this:

if [ condition ]; then
      Stuff here
fi

Answer 4

[[ -n $(df -h / | awk 'int($5)>6{print $5}') ]] && echo "Warning file system greater than 6%"