Why uniq -c output with space instead of \t?

Try this:

uniq -c | sed -r 's/^( *[^ ]+) +/\1\t/'

Try:

uniq -c text.file | sed -e 's/ *//' -e 's/ /\t/'

That will remove the spaces prior to the line count, and then replace only the first space with a tab.

To replace all spaces with tabs, use tr:

uniq -c text.file | tr ' ' '\t'

To replace all continuous runs of tabs with a single tab, use -s:

uniq -c text.file | tr -s ' ' '\t'