How to compare two dates in bash script?

Question

I am trying to compare todays date with the last modified date from a file.

DATE=$(date +"%F")

LASTMOD=$(stat $i -c %y);
LASTMOD_DATE=$(cut -d' ' -f1 <<<"$LASTMOD")

if [ "$LASTMOD_DATE" -ge "$DATE" ]; then
    printf "%-19s | " "$DATE"
else
    printf "%-19s | " "NO RECENT MOD"
fi

Currently this does not compare them properly and I think it's because LASTMOD_DATE is not actually a datetime so I get the error: "integer expression expected".

Answer 1

You can use the timestamp format date +%s and the -r option.

-r, --reference=FILE
         display the last modification time of FILE

like

if [ $(date +%s -r file) -ge $(date +%s) ]; then 
    # do something
fi

Answer 2

The best way to compare points of time (dates) is in seconds (since Epoch).

Changing the %y to %Y for stat will give the modification date of the file in seconds:

fileModifiedOn=$(stat $i -c %Y)

Today's date could be read either with (GNU) date with the format %s:

todayDate=$(date +'%s')

or, in Bash 5.0, with the variable EPOCHSECONDS:

todayDate=$EPOCHSECONDS

or, in older bash, with a (builtin) printf format:

todayDate=$(printf '%(%s)T')

Then, it is just a matter of a simple integer comparison:

if [[ "$fileModifiedOn" -gt "$todayDate" ]] then
    result=$todayDate
else
    result="NO RECENT MOD"
fi

printf "%-19s | " "$result"