▁text ▁in ▁otherwise ▁ambigu ous ▁cases ▁( e . g ., ▁${ foo } ing ). ▁ ▁Back slash ▁substitution ▁rep laces ▁a ▁back slash ▁followed ▁by ▁a ▁letter ▁with ▁another ▁character . ▁For ▁example , ▁\ n ▁is ▁replaced ▁by ▁a ▁newline . ▁Sub st itution ▁proceed s ▁left - to - right ▁in ▁a ▁single ▁scan ▁through ▁each ▁word . ▁Any ▁subst it uted ▁text ▁will ▁not ▁be ▁sc anned ▁again ▁for ▁possible ▁further ▁substitution s . ▁However , ▁any ▁number ▁of ▁substitution s ▁can ▁appear ▁in ▁a ▁single ▁word . ▁ ▁From ▁T cl ▁ 8 . 5 ▁on wards , ▁any ▁word ▁may ▁be ▁prefix ed ▁by ▁{ * }, ▁which ▁causes ▁the ▁word ▁to ▁be ▁split ▁apart ▁into ▁its ▁constitu ent ▁sub - words ▁for ▁the ▁purposes ▁of ▁building ▁the ▁command ▁inv ocation ▁( similar ▁to ▁the ▁, @ ▁sequence ▁of ▁L isp ' s ▁quasi quote ▁feature ). ▁ ▁As ▁a ▁consequence ▁of ▁these ▁rules , ▁the ▁result ▁of ▁any ▁command ▁may ▁be ▁used ▁as ▁an ▁argument ▁to ▁any ▁other ▁command . ▁Also , ▁there ▁is ▁no ▁operator ▁or ▁command ▁for ▁string ▁concaten ation , ▁as ▁the ▁language ▁concaten ates ▁directly . ▁Note ▁that , ▁unlike ▁in ▁Unix ▁command ▁shell s , ▁T cl ▁does ▁not ▁re parse ▁any ▁string ▁unless ▁explicitly ▁directed ▁to ▁do ▁so , ▁which ▁makes ▁interactive ▁use ▁more ▁cum bers ome , ▁but ▁script ed ▁use ▁more ▁predict able ▁( e . g ., ▁the ▁presence ▁of ▁spaces ▁in ▁fil en ames ▁does