▁argument ▁processing , ▁a ▁word ▁that ▁begins ▁with ▁a ▁double - quote ▁character ▁( ") ▁extends ▁to ▁the ▁next ▁double - quote ▁character . ▁Such ▁a ▁word ▁can ▁thus ▁contain ▁whitespace ▁and ▁sem icol ons ▁without ▁those ▁characters ▁being ▁interpreted ▁as ▁having ▁any ▁special ▁meaning ▁( i . e ., ▁they ▁are ▁treated ▁as ▁normal ▁text ▁characters ). ▁A ▁word ▁that ▁begins ▁with ▁an ▁opening ▁cur ly - brace ▁character ▁({ ) ▁extends ▁to ▁the ▁next ▁closing ▁cur ly - brace ▁character ▁( }). ▁Inside ▁cur ly ▁bra ces ▁all ▁forms ▁of ▁substitution ▁are ▁suppress ed ▁except ▁the ▁previously ▁mentioned ▁back slash - new line ▁elim ination . ▁W ords ▁not ▁en closed ▁in ▁either ▁construct ▁are ▁known ▁as ▁bare ▁words . ▁ ▁In ▁bare ▁and ▁double - qu oted ▁words , ▁three ▁types ▁of ▁substitution ▁may ▁occur : ▁ ▁Command ▁substitution ▁rep laces ▁the ▁contents ▁of ▁bal anced ▁square ▁brackets ▁with ▁the ▁result ▁of ▁evalu ating ▁the ▁script ▁contained ▁inside . ▁For ▁example , ▁[ expr ▁ 1 + 2 + 3 ] ▁is ▁replaced ▁by ▁the ▁result ▁of ▁evalu ating ▁the ▁contained ▁expression ▁( in ▁this ▁case ▁ 6 ). ▁ ▁Variable ▁substitution ▁rep laces ▁the ▁name ▁of ▁a ▁variable ▁prefix ed ▁with ▁a ▁doll ar ▁sign ▁with ▁the ▁contents ▁( or ▁value ) ▁of ▁the ▁variable . ▁For ▁example , ▁$ foo ▁is ▁replaced ▁by ▁the ▁contents ▁of ▁the ▁variable ▁called ▁" foo ". ▁The ▁variable ▁name ▁may ▁be ▁surrounded ▁by ▁cur ly ▁bra ces ▁to ▁separate ▁it ▁from ▁subsequent