Error on a disk space usage script

问题

I tried to modify a little script of checking disk space usage, and I faced the below error:

disk_space.sh: line 32: [: Use: integer expression expected

# Set alert limit, 90% we remove % for comparison
alert=90

# $1 is the partition name
# $5 is the used percentage
# Print the df -h, then loop and read the result 
df -h | awk '{ print $1 " " $5 }' | while read output;
do

#echo $output

# Get partition name
partition=$(echo $output | awk '{ print $1 }')
#echo 'Partition: ' $partition

# Used space with percentage
useSpPer=$(echo $output | awk '{ print $2}')
#echo 'Used space %: ' $useSpPer

#used space (remove percentage)
useSp=$(echo -n $useSpPer | head -c -1)
#echo 'Used space digit: ' $useSp

# Recap
#echo $useSp ' has ' $partition

# -ge is greatter than or equal
if [ $useSp -ge $alert ]; then # THIS LINE 32
echo $partition 'is running out of space with '$useSpPer

#else 
#echo 'Down'

fi
done

If anyone has an idea, appreciated it and thanks in advance

回答1:

Putting set -x at the top of your script so that it echoes each line before execution is a great way to debug shell scripts - you'll almost certainly find that one of those variables (used in the [ command) isn't being set as you expected.

That's good general advice but, for this problem where you've localised the problem, it's probably good enough (and certainly less verbose) to place this line before the line generating the problem:

echo "DEBUG [$useSp]"

If you do that, you'll find that the value you're checking is not a numeric value at all. That's because the output of df -h looks something like this:

Filesystem  Size  Used  Avail  Use%  Mounted on
/dev/sda1    48G  4.9G    40G   11%  /
/dev/sr0     71m   71M      0  100%  /media/cdrom0

That means that, for the first line, you'll be comparing the word Use against your limit and [ will not handle that well:

pax> if [ 20 -gt 10 ]; then echo yes; fi
yes
pax> if [ Use -gt 10 ]; then echo yes; fi
bash: [: Use: integer expression expected

The fix is fairly simple. Since you don't want to do anything with the first line, you can just use your existing awk to filter it out:

df -h | awk 'NR>1{print $1" "$5}' | while read output;
do
    ...

The NR>1 only processes record numbers two and so on, skipping the first one.

回答2:

Your useSp value is "Use" [non-numeric], so the -ge is trying to compare a string against an integer [and complaining].

UPDATE:

Per your request, there are a few ways to fix your script.

Fixing your existing script is one [see fix below]. But, this sort of string manipulation in bash can be a bit dicey as you're finding out.

Another is, since you're already using awk [in multiple places], recode the script to do most of the work in an awk script file. For example:

df -h | awk -f myawkscript.awk

But, awk is a bit ancient, so, ultimately, a newer language, such as perl or python would be the way to go long term. Powerful string manipulation and computation. They are compiled to VMs so they run faster. And, they have great diagnostic messages. IMO, rather than learn more awk, start learning perl/python [as, professionally, there is a demand for programming in these languages]

But, for an immediate fix to your existing script:
OLD: df -h | awk '{ print $1 " " $5 }' | while read output;
NEW: df -h | tail -n +2 | awk '{ print $1 " " $5 }' | while read output;

来源：https://stackoverflow.com/questions/34170648/error-on-a-disk-space-usage-script

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disk