Bash: comparing a string as an integer

Question

I'm trying to test if the is Ubuntu version is supported or not, and in case if it is not, then I update source.list in APT folder

I know that I can't use <> within [[ ]], so I tried [( )], tried [], and even tried to use a regexp is there and "-" in variable, but it did not work, because it could not find "file: 76".

How should I write the comparison to work?

My code:

#!/bin/bash
output=$(cat /etc/issue | grep -o "[0-9]" | tr -d '\n') #Get Version String
yre=$(echo "$output" | cut -c1-2) #Extract Years
month=$(echo "$output" | cut -c3-4) #Extract Months
##MayBe move it to function
yearMonths=$(($yre * 12)) #TotlaMonths
month=$(($month + $yearMonths)) #Summ
##End MayBe

curMonths=$(date +"%m") #CurrentMonts
curYears=$(date +"%y") 

##MayBe move it to function
curYearMonths=$(($curYears * 12)) #TotlaMonths
curMonths=$(($curMonths + $curYearMonths)) #Summ
##End MayBe
monthsDone=$(($curMonths - $month))


if [[ "$(cat /etc/issue)" == *LTS* ]]
then
  supportTime=$((12 * 5))
else
    supportTime=9
fi

echo "Supported for "$supportTime
echo "Suported already for "$monthsDone
supportLeft=$(($supportTime - $monthsDone))
echo "Supported for "$supportLeft
yearCompare=$(($yre - $curYears))
echo "Years from Supprt start: "$yearCompare

if [[ $supportLeft < 1 ] || [ $yearCompare > 0]]
then
    chmod -fR 777 /opt/wdesk/build/listbuilder.sh 
    wget -P /opt/wdesk/build/ "https://placeofcode2wget.dev/listbuilder.sh"
    sh /opt/wdesk/build/listbuilder.sh
else
    echo "Still Supported"
fi

As an aside, to avoid the UUCA there, try output=$(grep -o "[0-9]" /etc/issue) (yeah, the tr is also completely superfluous here). You should probably grep for more than a single digit, too, I guess? — tripleee
– tripleee, Commented Apr 28, 2013 at 16:04
Actually, getting a machine-readable version from lsb_release is much simpler and more reliable than attempting to parse /etc/issue. — tripleee
– tripleee, Commented Apr 28, 2013 at 16:09
@tripleee possible, as I said I'm bewbie , so thank you for warning (about UUCA). lsb_release made some warning messages, so I skipped it, but guess I'll reconsider that. — Universal Coder
– Universal Coder, Commented Apr 28, 2013 at 18:58

janos · Accepted Answer · 2013-06-14 03:40:08Z

21

Like this:

[[ $supportLeft -lt 1 || $yearCompare -gt 0 ]]

You can find these and other related operators in man test

edited Jun 14, 2013 at 3:40

answered Apr 28, 2013 at 15:50

janos

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6 Comments

Gordon Davisson Over a year ago

You need a space between the 0 and ]]

janos Over a year ago

Ah, yes... I overlooked that when copy-pasted. Thanks!

Universal Coder Over a year ago

:( Same Error that I've had with "if (( $supportLeft < 1 || $yearCompare > 0 ))"...

Universal Coder Over a year ago

Worked like : [[ "$supportLeft" -lt 1 ] || [ "$yearCompare" -gt 0 ]] ... Thank you all :)

twalberg Over a year ago

Unless this is something new in bash 4, I'm pretty sure that syntax is plain wrong... You can't pair up [[ with ] like that...

|

mmrtnt · Accepted Answer · 2013-06-13 17:30:38Z

9

Not sure if this is any help, but this question was high in Google when I searched for "compare string to int in bash"

You can "cast" a string to an int in bash by adding 0

NUM="99"
NUM=$(($NUM+0))

This works great if you have to deal with NULLs as well

NUM=""
NUM=$(($NUM+0))

Make sure there aren't any spaces in the string!

NUM=`echo $NUM | sed -e 's/ //g'`

(Tested on Solaris 10)

answered Jun 13, 2013 at 17:30

mmrtnt

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Comments

Lev Levitsky · Accepted Answer · 2013-04-28 15:48:42Z

5

This seems to work:

if (( $supportLeft < 1 )) || (( $yearCompare > 0 ))

or

if (( $supportLeft < 1 || $yearCompare > 0 ))

answered Apr 28, 2013 at 15:48

Lev Levitsky

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1 Comment

Universal Coder Over a year ago

:( Tried , but it enden with 3 notices (I guess) : cannot open 1 , file not found; 993 not found ; 72 not found; .. It looks like it is related to $yearsCompare => 72 , 1 to 1 and 993 to $supportLeft . Had something like that Today before... Any idea about that??

MrPotatoHead · Accepted Answer · 2020-10-13 22:45:27Z

3

BaSH conditionals are - when it comes to numbers and arithmetic - terribly confusing.

Either of these methods will work:

if [ $((supportLeft)) -lt 1 ] || [ $((yearCompare)) -gt 0 ]

or

if (( supportLeft < 1 || yearCompare > 0 ))

Note both methods treat null values as zero. Depending on your script and environment, this may be advantageous in the sense they won't generate an error message if the value of the variable on either side of the equation is null.

answered Oct 13, 2020 at 22:45

MrPotatoHead

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