Can I monitor the progress of importing a large .sql file in sqlite3 using zenity --progress?
The sqlite3 tool does not output such numbers.

You would have to write some script that feeds the lines of the import file into sqlite3, and at the same time feeds the percentage numbers into zenity. Try something like this:

#!/bin/bash
maxlines=$(wc -l &lt; import_file.sql)
exec 3&gt; &gt;(zenity --progress --auto-close)
counter=0
while IFS= read -r line; do
    echo "$line"
    counter=$(($counter+1))
    echo $(($counter * 100 / $maxlines)) &gt;&amp;3
done &lt; import_file.sql


Call it with thescript | sqlite3 dbfile.