printf '%*s\n' "${COLUMNS:-$(tput cols)}" '' | tr ' ' -

# or 

stty size | perl -ale 'print "-"x$F[1]'

僕は以下のように関数定義してデリミタ指定できるようにしてます。

horizonal_line(){
  : horizonal_line [delimiter]
  : e.g. horizonal_line "="
  # stty size | perl -ale 'print "-"x$F[1]'
  stty size | perl -ale "print \"${1:-"-"}\"x\$F[1]"
}

$ horizonal_line "*"
***********************************************************************************************
$ horizonal_line "="
===============================================================================================
$ horizonal_line "+"
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
$ horizonal_line "#"
###############################################################################################
$ horizonal_line
-----------------------------------------------------------------------------------------------