Issue comparing to strings in BASH

Question

I need to make a bash script to compare the space of a vg on redhat servers. What I have so far is:

#!/bin/bash

##VARS
CMD=$(vgs | grep vgSoft | awk -F" " '{print $7}' | awk -F"<" '{print $2}'| awk -F"g" '{print $1}')
SPACE="10.00"

if [[ "$CMD" < "$SPACE" ]]; then
    echo "It's not enough space, you must extend the VG"
    echo "Space is equal to: $CMD GB"
elif [[ "$CMD" == "$SPACE" ]]; then
    echo "It's enough space but consider extend the VG"
elif [[ "$CMD" > "$SPACE" ]]; then
    echo "It's enough space"
    echo "Space is equal to: $CMD GB"
fi

What do I do with this command is obtaing the output of volume groups and parse the data for obtain the desired value vgs | grep vgSoft | awk -F" " '{print $7}' | awk -F"<" '{print $2}'| awk -F"g" '{print $1}' and save it to the CMD variable. Where the output of vgs command is:

[root@server~]# vgs
  VG     #PV #LV #SN Attr   VSize   VFree
  vgSoft   2  13   0 wz--n-  71.99g <26.14g
  vgSys    1  12   0 wz--n- <63.51g <36.52g

So in this case, the result of my CMD variable is 26.14 And I'm making the comparison with the value 10.00 (which is assigned to the SPACE variable).

But I'm having an issue comparing the strings, because is the output of vgs command is for example 9.46 the script says me that "It's enough space" when the output should be "It's not enough space, you must extend the VG". As far I remember I don't be able to use the operators "eq" "gt" "ne" because I'm comparing to strings and not integer values.

Answer 1

With your shown samples, please try following awk code. We can do all this in single awk.

We have an awk variable named space where I have defined value as 10 as per shown attempts of OP, one could change it as per need.

vgs | awk -v space="10" '
FNR==1 || !/vgSoft/{ next }
{
  value=substr($7,2,length($7)-1)+0
}
value<space { 
  print "It\047s not enough space, you must extend the VG"
  next
}
value==space{
  print "It\047s enough space but consider extend the VG"
  next
}
value>space {
  print "It\047s enough space"
}
'

OR in case you have 7th field in lines which could OR couldn't have starting < in its value so to deal with these kind of situations please try following awk code.

vgs | awk -v space="10" '
FNR==1 || !/vgSoft/{ next }
{
  sub(/^</,"",$7)
  value=$7+0
}
value<space { 
  print "It\047s not enough space, you must extend the VG"
  next
}
value==space{
  print "It\047s enough space but consider extend the VG"
  next
}
value>space {
  print "It\047s enough space"
}
'

Explanation: Running vgs command first and sending its standard output as a standard input to awk program. In awk program creating variable space with value of 10 as per shown attempts. Then in main program, checking condition(s) if its line first line OR line does not contain vgSoft string then simply jump to next line. If a line contains vgSoft string then creating a variable named value which will have value from 7th field of current line(without < and g from 7th field), then using 3 conditions to check(if value is equal to OR lesser than OR grater than space or not) accordingly printing statements then.

Fair warning I don't have vgs command with me so I tested this code with putting your sample output of vgs command into an Input_file and running it against awk program and it worked fine for me.

Answer 2

You may just use the echo command in combination with bc for comparison as shown below

$ SPACE=10.00
$ CMD=9.46
$ echo "${CMD}>${SPACE}" | bc
0
$ CMD=10.46
$ echo "${CMD}>${SPACE}" | bc
1

Answer 3

Doing it in just awk:

vgs | awk -v space=10.00 '/vgSoft/ {
   free = substr($7, 2, length($7) - 2)+0 # Assumes the < and g will always be there
   if (free < space) {
     print "It'"'"'s not enough space, you must extend the VG"
     print "Space is equal to: " space " GB"
   } else if (free == space) {
     print "It'"'"'s enough space but consider extend the VG"
   } else {
     print "It'"'"'s enough space"
     print "Space is equal to: " space " GB"
   }
   exit
}'