Why is sed not recognizing \t as a tab?
Solution 1:
Not all versions of sed understand \t. Just insert a literal tab instead (press Ctrl-V then Tab).
Solution 2:
Using Bash you may insert a TAB character programmatically like so:
TAB=$'\t'
echo 'line' | sed "s/.*/${TAB}&/g"
echo 'line' | sed 's/.*/'"${TAB}"'&/g' # use of Bash string concatenation