Bash error: Integer expression expected - bash

Question

In the sections below, you'll see the shell script I am trying to run on a UNIX machine, along with a transcript.
When I run this program, it gives the expected output but it also gives an error shown in the transcript. What could be the problem and how can I fix it?
First, the script:
#!/usr/bin/bash
while read A B C D E F
do
E=`echo $E | cut -f 1 -d "%"`
if test $# -eq 2
then
I=`echo $2`
else
I=90
fi
if test $E -ge $I
then
echo $F
fi
done
And the transcript of running it:
$ df -k | ./filter.sh -c 50
./filter.sh: line 12: test: capacity: integer expression expected
/etc/svc/volatile
/var/run
/home/ug
/home/pg
/home/staff/t
/packages/turnin
$ _

Answer 1

Before the line that says:
if test $E -ge $I
temporarily place the line:
echo "[$E]"
and you'll find something very much non-numeric, and that's because the output of df -k looks like this:
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/sdb1 954316620 212723892 693109608 24% /
udev 10240 0 10240 0% /dev
: :
The offending line there is the first, which will have its fifth field Use% turned into Use, which is definitely not an integer.
A quick fix may be to change your usage to something like:
df -k | sed -n '2,$p' | ./filter -c 50
or:
df -k | tail -n+2 | ./filter -c 50
Either of those extra filters (sed or tail) will print only from line 2 onwards.
If you're open to not needing a special script at all, you could probably just get away with something like:
df -k | awk -vlimit=40 '$5+0>=limit&&NR>1{print $5" "$6}'
The way it works is to only operate on lines where both:
the fifth field, converted to a number, is at least equal to the limit passed in with -v; and
the record number (line) is two or greater.
Then it simply outputs the relevant information for those matching lines.
This particular example outputs the file system and usage (as a percentage like 42%) but, if you just want the file system as per your script, just change the print to output $6 on its own: {print $6}.
Alternatively, if you do the percentage but without the %, you can use the same method I used in the conditional: {print $5+0" "$6}.