ABC uses different symbols for ties and slurs, though most music publishers draw them with indistinguishable curved lines. The notation for ties is a hyphen ('-') after the first note. This should usually be used only between identical notes, though some software understands the use of ties between different notes. But most ABC software will give you a warning if the notes aren't the same.
Slurs are indicated with parentheses before the first note and after the second:
| (DE)FG (AB)cd |This is how you'd write the usual 2-1-1 "fiddle shuffle" bowing in a tune.
Slurs are also sometimes nested, with the longer (outer) pairs of parentheses used to indicate phrasing. This should work with most ABC software, though you might not hear the effect of the outer "phrase" parentheses from many ABC player programs
Copyright 2001, 2002 by John Chambers