If- else statement shell script

Question

I am writing a shell script to rotate a log file based on size leveraging the logrotate.conf utility.

#!/bin/bash 
FILENAME=/xyz/console.log  

    while :
    do  
        FILESIZE=$(du -h "$FILENAME")

        ####FILESIZE=$(stat -c%s "$FILENAME")

        if [[ $FILESIZE > 10K ]];
        then
            echo "$FILENAME is too large = $FILESIZE"
            echo "$(date ) is here"
            cd "/etc"
            $sudo logrotate -f logrotate.conf
            echo "$ Newer version of log file is created"
        else
            echo "Log limit is not reached"
        fi
    sleep 60s

done

exit 0

It is not printing else block ,even when the size is less than 10K. In all cases, it is executing the if block and rotating the logs even at 4.0K. Only when the log file is of zero bytes it is printing else part i.e.:

Log limit is not reached

Why not use stat or du (without -h)? The problem is that du will bring the file name too, unless you use cut -f 1. The ideal is to get the value in bytes and compare. — Valdeir Psr
– Valdeir Psr, Commented Dec 29, 2017 at 7:22

Gordon Davisson · Accepted Answer · 2017-12-29 07:34:17Z

3

The problem is that [[ > ]] is doing a string comparison (essentially, alphabetical order) rather than numeric comparison. So, for example, [[ 9 > 10 ]] is true, because the character "9" comes after "1" in ASCII sorting order. But switching to numeric comparisons (with (( > )) or [[ -gt ]]) won't work either, because the "numbers" you're comparing have unit suffixes ("B" for byte, "K" for kilobyte, etc, so 500B is less than 1K) and the output from du also includes the filename, which'd need to be striped before comparing.

This is much too much work. Just use stat to get a pure numeric result, and do numeric comparison on that. Oh, and you should stick to lower- or mixed-case variable names, to avoid accidentally using one of the ones that has special meaning to the shell (e.g. PATH):

...
filesize=$(stat -f %z "$filename")
if (( filesize > 10240 )); then
...

answered Dec 29, 2017 at 7:34

Gordon Davisson

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2 Comments

Soumik Bhattacharya Over a year ago

I have tried various options as suggested and modified the code as while : do FILESIZE=$(du "$FILENAME") #FILESIZE=$(stat -c%s "$FILENAME") #FILESIZE=$( du -b "$FILENAME" | cut -f1) if (( $FILESIZE > 1000000 )); then echo "$FILENAME is too large = $FILESIZE" echo "$(date ) is here" cd "/etc" $sudo logrotate -f logrotate.conf echo "$ Newer version of log file is created" else echo "Log limit is not reached" fi sleep 60s the log file in question is 96185 bytes..still getting rotated

Gordon Davisson Over a year ago

@SoumikBhattacharya Did you try the stat command I recommended? Also, have your script print the value of FILESIZE before checking it, so you can see what's actually happening.

user1934428 · Accepted Answer · 2017-12-29 07:27:11Z

1

You are using string comparision. For example, if the file size is 2K, 2K > 10K is true, because 2 comes alphabetically after 10.

Easiest solution would be to drop the -h option - which doesn't make much sense anyway, if you want to process the result further - and then use numerical comparision,

if (( FILESIZE > 10 ))
then

fi

answered Dec 29, 2017 at 7:27

user1934428

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2 Comments

Soumik Bhattacharya Over a year ago

I have tried various options as suggested and modified the code as while : do FILESIZE=$(du "$FILENAME") #FILESIZE=$(stat -c%s "$FILENAME") #FILESIZE=$( du -b "$FILENAME" | cut -f1) if (( $FILESIZE > 1000000 )); then echo "$FILENAME is too large = $FILESIZE" echo "$(date ) is here" cd "/etc" $sudo logrotate -f logrotate.conf echo "$ Newer version of log file is created" else echo "Log limit is not reached" fi sleep 60s the log file in question is 96185 bytes..still getting rotated

user1934428 Over a year ago

Post your modified code. Also, show the value of FILESIZE.

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