GNU Coreutil Date (outputs numbers in CLI but not in bash script)

Question

Whenever I run a command in bash CLI, I get the right output

date +%Y%-m%d%j%M%S
202111063103528

However, when I run this in a bash script, I am not getting a simple number that I can use in a later variable. I'm ultimately wanting to use this to backup old CSV files I've generated. e.g.

#Doesn't print out correct date
DATE='date +%Y%-m%d%j%M%S'
echo $DATE

# Ultimately, wanting to feed that $DATE string here 
if [ -f "$CSV_OUTFILE" ]; then
          echo "CSV file already exists. Renaming $CSV_OUTFILE to $CSV_OUTFILE.$DATE"
          mv $CSV_OUTFILE $CSV_OUTFILE.$DATE
          exit 1
fi

Answer 1

You assigned the string date +%Y%-m%d%j%M%S to $DATE. It contains a space, so using $DATE in mv without double quotes expands it to two words.

Use backquotes instead of quotes to capture the output of a command:

DATE=`date +%Y%-m%d%j%M%S`

Or, better, use the $(...) syntax (better because it can be nested):

DATE=$(date +%Y%-m%d%j%M%S)