while loop stops before false [duplicate]

This question already has an answer here:

Trying to zip up all logs except for one in a directory. I know there are other ways to accomplish what I'm trying to do, but I'm mainly curious as to WHY the following is happening.

I have the following script:

#!/usr/bin/env bash TOTAL=$(ls -lah ./*.log | wc -l) let "TOTAL--" COUNT=0 while [[ $COUNT < $TOTAL ]]; do gzip $(ls -1 | grep -v '.gz' | grep '.log' | head -n 1) let "COUNT++" echo "$TOTAL - $COUNT = $(($TOTAL-$COUNT))" sleep 2 done

To set up the environment for this, you could do something like:

cd mkdir tmp0 cd tmp0 touch test_1..20.log

Then put this script inside the same directory (yes, yes you could also just set a var to reference the directory too). Anyways, when set up like this and run, it stops while $COUNT is still less than $TOTAL:

$COUNT

$TOTAL

[ec2-user@ip-172-31-0-70 ~]$ cd [ec2-user@ip-172-31-0-70 ~]$ mkdir tmp0 [ec2-user@ip-172-31-0-70 ~]$ cd tmp0/ [ec2-user@ip-172-31-0-70 tmp0]$ touch test_1..20.log [ec2-user@ip-172-31-0-70 tmp0]$ mv ../myscript.sh . [ec2-user@ip-172-31-0-70 tmp0]$ ll total 4 -rwxrwxr-x 1 ec2-user ec2-user 245 Aug 9 11:45 myscript.sh -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_10.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_11.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_12.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_13.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_14.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_15.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_16.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_17.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_18.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_19.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_1.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_20.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_2.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_3.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_4.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_5.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_6.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_7.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_8.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_9.log [ec2-user@ip-172-31-0-70 tmp0]$ ./myscript.sh 19 - 1 = 18 19 - 2 = 17 [ec2-user@ip-172-31-0-70 tmp0]$ ll total 12 -rwxrwxr-x 1 ec2-user ec2-user 245 Aug 9 11:45 myscript.sh -rw-rw-r-- 1 ec2-user ec2-user 32 Aug 9 12:24 test_10.log.gz -rw-rw-r-- 1 ec2-user ec2-user 32 Aug 9 12:24 test_11.log.gz -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_12.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_13.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_14.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_15.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_16.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_17.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_18.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_19.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_1.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_20.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_2.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_3.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_4.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_5.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_6.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_7.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_8.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:24 test_9.log [ec2-user@ip-172-31-0-70 tmp0]$ [ec2-user@ip-172-31-0-70 tmp0]$ [ec2-user@ip-172-31-0-70 tmp0]$ bash -x ./myscript.sh ++ wc -l ++ ls -lah ./test_12.log ./test_13.log ./test_14.log ./test_15.log ./test_16.log ./test_17.log ./test_18.log ./test_19.log ./test_1.log ./test_20.log ./test_2.log ./test_3.log ./test_4.log ./test_5.log ./test_6.log ./test_7.log ./test_8.log ./test_9.log + TOTAL=18 + let TOTAL-- + COUNT=0 + [[ 0 < 17 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_12.log + let COUNT++ + echo '17 - 1 = 16' 17 - 1 = 16 + sleep 2 + [[ 1 < 17 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_13.log + let COUNT++ + echo '17 - 2 = 15' 17 - 2 = 15 + sleep 2 + [[ 2 < 17 ]] [ec2-user@ip-172-31-0-70 tmp0]$

You can see that it stops while 2 is less than 17. But, if when setting up the tmp0 directory, you only touch 1 through 9 instead of double digits, the while loop runs all the way through:

[ec2-user@ip-172-31-0-70 tmp0]$ rm test* [ec2-user@ip-172-31-0-70 tmp0]$ ll total 4 -rwxrwxr-x 1 ec2-user ec2-user 245 Aug 9 11:45 myscript.sh [ec2-user@ip-172-31-0-70 tmp0]$ touch test_1..9.log [ec2-user@ip-172-31-0-70 tmp0]$ ll total 4 -rwxrwxr-x 1 ec2-user ec2-user 245 Aug 9 11:45 myscript.sh -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_1.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_2.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_3.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_4.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_5.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_6.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_7.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_8.log -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_9.log [ec2-user@ip-172-31-0-70 tmp0]$ bash -x ./myscript.sh ++ wc -l ++ ls -lah ./test_1.log ./test_2.log ./test_3.log ./test_4.log ./test_5.log ./test_6.log ./test_7.log ./test_8.log ./test_9.log + TOTAL=9 + let TOTAL-- + COUNT=0 + [[ 0 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_1.log + let COUNT++ + echo '8 - 1 = 7' 8 - 1 = 7 + sleep 2 + [[ 1 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_2.log + let COUNT++ + echo '8 - 2 = 6' 8 - 2 = 6 + sleep 2 + [[ 2 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_3.log + let COUNT++ + echo '8 - 3 = 5' 8 - 3 = 5 + sleep 2 + [[ 3 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_4.log + let COUNT++ + echo '8 - 4 = 4' 8 - 4 = 4 + sleep 2 + [[ 4 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_5.log + let COUNT++ + echo '8 - 5 = 3' 8 - 5 = 3 + sleep 2 + [[ 5 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_6.log + let COUNT++ + echo '8 - 6 = 2' 8 - 6 = 2 + sleep 2 + [[ 6 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_7.log + let COUNT++ + echo '8 - 7 = 1' 8 - 7 = 1 + sleep 2 + [[ 7 < 8 ]] ++ head -n 1 ++ grep .log ++ grep -v .gz ++ ls -1 + gzip test_8.log + let COUNT++ + echo '8 - 8 = 0' 8 - 8 = 0 + sleep 2 + [[ 8 < 8 ]] [ec2-user@ip-172-31-0-70 tmp0]$ ll total 36 -rwxrwxr-x 1 ec2-user ec2-user 245 Aug 9 11:45 myscript.sh -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_1.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_2.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_3.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_4.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_5.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_6.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_7.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_8.log.gz -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_9.log [ec2-user@ip-172-31-0-70 tmp0]$ bash -x ./myscript.sh ++ wc -l ++ ls -lah ./test_9.log + TOTAL=1 + let TOTAL-- + COUNT=0 + [[ 0 < 0 ]] [ec2-user@ip-172-31-0-70 tmp0]$ ll total 36 -rwxrwxr-x 1 ec2-user ec2-user 245 Aug 9 11:45 myscript.sh -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_1.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_2.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_3.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_4.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_5.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_6.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_7.log.gz -rw-rw-r-- 1 ec2-user ec2-user 31 Aug 9 12:28 test_8.log.gz -rw-rw-r-- 1 ec2-user ec2-user 0 Aug 9 12:28 test_9.log [ec2-user@ip-172-31-0-70 tmp0]$

I'm just wondering why. I'm sure it's probably something stupid simple, but I'm just not seeing it. At first I thought it was because bash on macOS was "special", but then I tried it on Amazon Linux, and experienced the same thing.

Thanks in advance.

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

[[ $count < $total ]] is comparing ASCII value of strings, so 10 is less than 2. Use (( count < total )), [[ $count -lt $total ]], or [ "$count" -lt "$total" ].
– Charles Duffy
Aug 9 at 19:40

[[ $count < $total ]]

10

2

(( count < total ))

[[ $count -lt $total ]]

[ "$count" -lt "$total" ]

Thank you @CharlesDuffy. I apologize for not doing a better job searching. I did search, but apparently not for the correct terms.
– amoreno
Aug 9 at 20:22

1 Answer
1

You are doing string comparisons.

[[ '2' > '19' ]] && echo "true"

will output

true

Use integer arithmetic.

(( 2 > 19 )) && echo "true"

will not output anything.

In How to Answer, see the section "Answer Well-Asked Questions", particularly the bullet point regarding questions which "have already been asked and answered many times before".
– Charles Duffy
Aug 9 at 19:42

I agree, I'm sure it is. I don't know of which question it is a duplicate, though, and I'm not sure what to search to find it. I did a best effort google search and the first 3 results were not ones I'd like to as a duplicate. At that point, this took 30s to write and was faster to answer the question than finding the right question to link to
– jeremysprofile
Aug 9 at 19:43

I understand, but pointing someone to the most complete answer is better for long-term quality than being fast/first. (That said, I've sometimes made a habit of adding a community-wiki answer when I know something is duplicate but can rattle off a quick solution, and closing as dupe a few minutes later after spending the time to find a good list; community-wiki means others are allowed and encouraged to edit that answer to tune it for the individual OP, whereas the list of canonical answers points others with similar questions towards a more complete and canonical source).
– Charles Duffy
Aug 9 at 19:50

@CharlesDuffy, so in the future, is it better to "give up" on a question that I can't find a link to, leave a comment that basically answers the question, or provide an answer? If I was a new user, linking to a question that I reasonably would not have known how to search for and marking mine as a duplicate would be irritating, especially as (I believe) it counts as "bad question" in SO, and it threatens to suspend you if you have a record of it. This happened to me on a few questions when I first joined.
– jeremysprofile
Aug 9 at 19:54

@CharlesDuffy, I will keep the community wiki option in mind so I don't appear to be trawling for points.
– jeremysprofile
Aug 9 at 19:55

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while loop stops before false [duplicate]

while loop stops before false [duplicate]

1 Answer
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