📄 acd.1
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4538(removed)S4916(from)S5138(the)S7296 V(input.)231 1440 A1721(The)S1903(sequence)S10 B2297(\\n)S10 R2406(is)S2498(changed)S2858(to)S2961(a)S3031(newline.)S7903 V720(Page)S941(1)S4455(September)S4911(13,)S(1996)200 5061 A8143 VEP%%Page: 2 2BP/slant 0 def/height 0 def480 V10 R720(ACD)S941(\()S983(1)S1041(\))S2696(Eighth)S(Edition)296 2989 A4906(ACD)S5127(\()S5169(1)S5227(\))S960 V(Substitutions)524 1080 A1080 V1440(A)S(substitution)468 1546 A2048(\(henceforth)S2547(called)S2822('subst'\))S3164(is)S3265(formed)S3590(with)S3803(a)S10 B3882($)S10 R3932(,)S3991(e.g.)S10 B4195($opt)S10 R4385(,)S10 B4444($PATH)S10 R4774(,)S10 B4833(${lib})S10 R5075(,)S10 B5134($)S10 Y5184(*)S5186(*)S10 R5236(.)S1200 V1440(The)S1633(variable)S1994(name)S2248(after)S2470(the)S10 B2629($)S10 R2714(is)S2816(made)S3069(of)S3188(letters,)S3495(digits)S3753(and)S(underscores,)506 3933 A4474(or)S4593(any)S4773(sequence)S5177(of)S1320 V1440(characters)S1884(between)S2254(parentheses)S2759(or)S(braces,)283 2878 A3196(or)S3315(a)S3395(single)S3670(other)S3912(character.)S4368(A)S4476(subst)S4717(indicates)S5110(that)S1440 V1440(the)S1588(value)S1831(of)S1940(the)S2088(named)S2381(variable)S2731(must)S2951(be)S(substituted)435 3071 A3531(in)S3634(the)S3782(list)S3930(or)S4039(string)S4293(when)S4536(fully)S4751(evaluated.)S1608 V1080(Letters)S1440(Letters)S1746(are)S1895(the)S2043(single)S2308(characters)S2743(that)S2919(would)S3195(make)S3438(up)S3563(a)S3633(word.)S1776 V1080(Operators)S1896 V1440(The)S1633(characters)S10 B2079(=)S10 R2136(,)S10 B2197(+)S10 R2254(,)S10 B-12315(-)S10 R2372(,)S10 Y2433(*)S2435(*)S10 R2485(,)S10 B2546(<)S10 R2603(,)S2664(and)S10 B2845(>)S10 R2938(are)S3098(the)S3257(operators.)S3718(The)S3911(\256rst)S4104(four)S4308(must)S4540(be)S(surrounded)452 4672 A5161(by)S2016 V(whitespace)448 1440 A1921(if)S2016(they)S2222(are)S2378(to)S2488(be)S2615(seen)S2826(as)S2942(special)S3254(\(they)S3493(are)S3649(often)S3888(used)S4104(in)S4214(arguments\).)S4749(The)S4938(last)S5110(two)S2136 V1440(are)S1589(always)S1894(special.)S2304 V1080(Lists)S1440(One)S1636(line)S1815(of)S1927(objects)S2240(in)S2346(the)S2497(description)S2972(\256le)S3129(forms)S3392(a)S3465(list.)S3666(Put)S3828(parentheses)S(around)279 4326 A4633(it)S4718(and)S(you)150 4892 A5071(have)S2424 V1440(a)S1510(sublist.)S1847(The)S2029(values)S2311(of)S2420(variables)S2809(are)S2958(lists.)S2592 V1080(Strings)S1440(Anything)S1852(that)S2036(is)S2136(not)S2297(yet)S2453(a)S2531(word)S2771(is)S2871(a)S2949(string.)S3261(All)S3423(it)S3512(needs)S3774(is)S3874(that)S4058(the)S4214(substs)S4492(in)S4603(it)S4692(are)S4850(evaluated,)S2712 V1440(e.g.)S10 B($LIBPATH/lib$key.a)919 1646 A10 R2565(.)S2651(A)S2760(single)S3036(subst)S3278(doesn't)S3610(make)S3863(a)S3943(string,)S4232(it)S4323(expands)S4687(to)S4800(a)S4880(list.)S5088(You)S2832 V1440(need)S1663(at)S1769(least)S1987(one)S2165(letter)S2406(or)S2523(other)S2763(subst)S3002(next)S3208(to)S3319(it.)S3458(Strings)S3777(\(and)S3990(words\))S4304(may)S4511(also)S4707(be)S4836(formed)S5161(by)S2952 V1440(enclosing)S1850(them)S2076(in)S(double)273 2179 A(quotes.)287 2477 A2814(Only)S10 B3040(\\)S10 R3093(and)S10 B3263($)S10 R3338(keep)S3553(their)S3763(special)S4068(meaning)S4439(within)S(quotes.)287 4721 A3120 V870(E)S872(Ev)S936(va)S988(al)S1035(lu)S1065(ua)S1117(at)S1164(ti)S1194(io)S1224(on)S1276(n)S3240 V1080(One)S1276(thing)S1510(has)S1672(to)S1778(be)S1902(carefully)S(understood:)474 2290 A(Substitutions)524 2793 A3346(are)S3499(delayed)S(until)184 3841 A4054(the)S4206(last)S4375(possible)S4733(moment,)S5116(and)S3360 V1080(description)S1573(\256les)S1787(make)S2051(heavy)S2337(use)S2517(of)S2647(this.)S2888(Only)S3135(if)S3243(a)S3334(subst)S3586(is)S3699(tainted,)S4044(either)S(because)319 4320 A4684(its)S4824(variable)S5194(is)S3480 V1080(declared)S1448(local,)S1696(or)S(because)319 1807 A2153(a)S2225(subst)S2458(in)S2563(its)S2685(variable's)S3110(value)S3355(is)S3449(tainted,)S3775(is)S3869(it)S3952(immediately)S(substituted.)460 4482 A4994(So)S5127(if)S5216(a)S3600 V1080(list)S1233(is)S1330(assigned)S1706(to)S1814(a)S1889(variable)S2244(then)S2447(this)S2622(list)S2775(is)S2872(only)S3080(checked)S3440(for)S3588(tainted)S3892(substs.)S4217(Those)S4492(substs)S4766(are)S(replaced)342 4919 A3720 V1080(by)S1205(the)S1353(value)S1596(of)S1705(their)S1915(variable.)S2315(This)S2519(is)S2611(called)S2877(partial)S3160(evaluation.)S3888 V1080(Full)S1267(evaluation)S1711(expands)S2065(all)S2191(substs,)S2486(the)S2634(list)S2782(is)S2874(\257attened,)S3271(i.e.)S3419(all)S3545(parentheses)S4040(are)S4189(removed)S4566(from)S4787(sublists.)S4056 V1080(Implosive)S1510(evaluation)S1957(is)S2052(the)S2203(last)S2371(that)S2550(has)S2712(to)S2818(be)S(done)195 2941 A3164(to)S3270(a)S3343(list)S3494(before)S3780(it)S3864(can)S4032(be)S4155(used)S4368(as)S4481(a)S4555(command)S4980(to)S5087(exe-)S4176 V1080(cute.)S1330(The)S1519(substs)S1796(within)S2085(a)S2162(string)S2423(have)S2645(been)S2867(evaluated)S3285(to)S3395(lists)S3589(after)S3807(full)S3979(expansion,)S4443(but)S4603(a)S4680(string)S4940(must)S5166(be)S4296 V1080(turned)S1363(into)S1545(a)S1616(single)S1882(word,)S2140(not)S2294(a)S2366(list.)S2566(To)S2705(make)S2950(this)S3122(happen,)S3464(a)S3536(string)S3792(is)S3886(\256rst)S4070(exploded)S4465(to)S4570(all)S4698(possible)S5054(com-)S4416 V1080(binations)S1482(of)S1600(words)S(choosing)362 1880 A2276(one)S2455(member)S2819(of)S2937(the)S3094(lists)S3290(within)S3581(the)S3738(string.)S4051(These)S4326(words)S4606(are)S4764(tried)S4983(one)S5161(by)S4536 V1080(one)S1254(to)S1361(see)S1519(if)S1610(they)S1812(exist)S2031(as)S2144(a)S2218(\256le.)S2426(The)S2612(\256rst)S2798(one)S2972(that)S3153(exists)S3412(is)S3509(taken,)S3782(if)S(none)195 3874 A4099(exists)S4358(than)S4561(the)S4714(\256rst)S4901(choice)S5194(is)S4656 V1080(used.)S1343(As)S1483(an)S1606(example,)S2000(assume)S10 B2324(LIBPATH)S10 R2805(equals)S10 B(\(/lib)174 3090 A(/usr/lib\))342 3292 A10 R3634(,)S10 B3687(key)S10 R3866(is)S10 B3961(\(c\))S10 R4102(and)S10 B4275(key)S10 R4454(happens)S4811(to)S4917(be)S5040(local.)S4776 V1080(Then)S1312(we)S1455(have:)S4944 V10 B("$LIBPATH/lib$key.a")1031 1440 A5112 V10 R1080(before)S1363(evaluation,)S5280 V10 B("$LIBPATH/lib\(c\).a")943 1440 A5448 V10 R1080(after)S1291(partial)S1574(evaluation,)S5616 V10 B("\(/lib/libc.a)490 1440 A(/usr/lib/libc.a\)")658 1955 A5784 V10 R1080(after)S1291(full)S1456(evaluation,)S1925(and)S2095(\256nally)S5952 V10 B(/usr/lib/libc.a)568 1440 A6120 V10 R1080(after)S1291(implosion,)S1742(if)S1829(the)S1977(\256le)S2131(exists.)S6288 V870(O)S872(Op)S947(pe)S999(er)S1046(ra)S1082(at)S1129(to)S1159(or)S1211(rs)S1247(s)S6408 V1080(The)S1262(operators)S1662(modify)S1977(the)S2125(way)S2318(evaluation)S2762(is)S(done)195 2854 A3074(and)S3244(perform)S3594(a)S3664(special)S3969(function)S4329(on)S4454(a)S4524(list:)S6576 V10 Y1080(*)S1082(*)S10 R1440(Forces)S1741(full)S1913(evaluation)S2364(on)S2496(all)S2629(the)S2784(list)S2939(elements)S3329(following)S3752(it.)S3890(Use)S4079(it)S4168(to)S4279(force)S(substitution)468 4520 A5021(of)S5138(the)S6696 V1440(current)S1751(value)S1994(of)S2103(a)S2173(variable.)S2573(This)S2777(is)S2869(the)S3017(only)S3220(operator)S3581(that)S3757(forces)S4029(immediate)S4479(evaluation.)S6864 V10 B1080(+)S10 R1440(When)S1705(a)S10 B1775(+)S10 R1857(exists)S2111(in)S2214(a)S2285(list)S2434(that)S2611(is)S2704(fully)S2920(evaluated,)S3357(then)S3556(all)S3683(the)S3832(elements)S4216(before)S4500(the)S10 B4649(+)S10 R4732(are)S4882(imploded)S6984 V1440(and)S1611(all)S1738(elements)S2122(after)S2334(the)S10 B2483(+)S10 R2566(are)S2715(imploded)S3119(and)S3289(added)S3554(to)S3657(the)S3805(list)S3953(if)S4040(they)S4238(are)S4387(not)S4540(already)S4862(in)S4965(the)S5113(list.)S7104 V1440(So)S1578(this)S1755(operator)S2124(can)S2297(be)S2425(used)S2642(either)S2905(for)S3056(set)S(addition,)354 3201 A3588(or)S3705(to)S3816(force)S4057(implosive)S4486(expansion)S4926(within)S5216(a)S7224 V1440(sublist.)S7392 V10 B-11080(-)S10 R1440(Like)S10 B1650(+)S10 R1707(,)S1757(except)S2045(that)S2221(elements)S2604(after)S2815(the)S10 B-12963(-)S10 R3045(are)S3194(removed)S3571(from)S3792(the)S3940(list.)S7903 V720(September)S1176(13,)S(1996)200 1326 A4990(Page)S5211(2)S8143 VEP%%Page: 3 3BP/slant 0 def/height 0 def480 V10 R720(ACD)S941(\()S983(1)S1041(\))S2696(Eighth)S(Edition)296 2989 A4906(ACD)S5127(\()S5169(1)S5227(\))S960 V1080(The)S1263(set)S1401(operators)S1802(can)S1968(be)S2089(used)S2299(to)S2403(gather)S2681(options)S3003(that)S3181(exclude)S(each)185 3521 A3733(other)S3967(or)S4078(for)S4223(their)S4435(side)S4624(effect)S4882(of)S4993(implo-)S1080 V1080(sive)S1267(expansion.)S1749(You)S1947(may)S2145(want)S2366(to)S2469(write:)S1248 V10 B1440(cpp)S10 B-11622(-)S10 B1679(I$LIBPATH/include)S1416 V10 R1080(to)S1187(call)S1362(cpp)S1537(with)S1746(an)S1871(extra)S2103(include)S2429(directory,)S2848(but)S10 B3006($LIBPATH)S10 R3539(is)S3636(expanded)S4051(using)S4298(a)S4373(\256lename)S4750(starting)S5082(with)S1536 V10 B-11080(-)S10 B1137(I)S10 R1205(so)S1323(this)S1497(won't)S1761(work.)S2047(Given)S2322(that)S2502(any)S2676(problem)S3040(in)S3147(Computer)S3578(Science)S3921(can)S4090(be)S4214(solved)S4505(with)S4712(an)S4835(extra)S5065(level)S1656 V1080(of)S1189(indirection,)S1675(use)S1834(this)S2004(instead:)S1824 V10 B1440(cpp)S10 B-11622(-)S10 B1679(I$INCLUDE)S1944 V1440(INCLUDE)S1930(=)S2012($LIBPATH/include)S2882(+)S2112 V10 R870(S)S872(Sp)S930(pe)S982(ec)S1029(ci)S1076(ia)S1106(al)S1153(l)S1208(V)S1210(Va)S1285(ar)S1332(ri)S1368(ia)S1398(ab)S1445(bl)S1497(le)S1527(es)S1574(s)S2232 V1080(There)S1345(are)S1498(three)S1729(special)S2038(variables)S2431(used)S2644(in)S2751(a)S2825(description)S3301(\256le:)S10 B3487($)S10 Y3537(*)S3539(*)S10 R3589(,)S10 B3643($<)S10 R3750(,)S3804(and)S10 B3978($>)S10 R4085(.)S4164(These)S4434(variables)S4827(are)S4981(always)S2352 V1080(local)S1301(and)S1471(mostly)S1769(read-only.)S2230(They)S(will)157 2462 A2644(be)S2764(explained)S3180(later.)S2520 V870(A)S872(A)S972(P)S974(Pr)S1032(ro)S1068(og)S1120(gr)S1172(ra)S1208(am)S1255(m)S2640 V1080(The)S1272(lists)S1469(in)S1582(a)S1662(description)S2144(\256le)S2308(form)S2539(a)S2619(program)S2995(that)S3181(is)S3283(executed)S3676(from)S3907(the)S4065(\256rst)S4257(to)S4370(the)S4528(last)S4703(list.)S4911(The)S5104(\256rst)S2760 V1080(word)S1317(in)S1425(a)S1499(list)S1651(may)S1853(be)S(recognized)442 1977 A2448(as)S2561(a)S(builtin)262 2635 A2926(command)S3351(\(only)S3592(if)S3683(the)S3835(\256rst)S4021(list)S4173(element)S4521(is)S4617(indeed)S4914(simply)S5216(a)S2880 V1080(word.\))S1399(If)S1495(it)S1579(is)S1674(not)S1830(a)S(builtin)262 1903 A2193(command)S2617(then)S2818(the)S2969(list)S3120(is)S3215(imploded)S3622(and)S3795(used)S4007(as)S4119(a)S8 R4187(UNIX)S10 R4416(command)S4840(with)S5048(argu-)S3000 V1080(ments.)S3168 V1080(Indentation)S1569(\(by)S1734(tabs)S1927(or)S(spaces\))297 2042 A2370(is)S2468(not)S2627(just)S2803(makeup)S3152(for)S3301(a)S3378(program,)S3776(but)S3936(are)S4092(used)S4308(to)S(group)234 4418 A4684(lines)S4906(together.)S3288 V1080(Some)S(builtin)262 1334 A1621(commands)S2081(need)S2296(a)S(body.)225 2366 A2641(These)S(bodies)262 2907 A3194(are)S3343(simply)S3641(lines)S3856(at)S3954(a)S4024(deeper)S4318(indentation.)S3456 V1080(Empty)S1384(lines)S1610(are)S1770(not)S(ignored)307 1934 A2277(either,)S2568(they)S2777(have)S3003(the)S3162(same)S3405(indentation)S3893(level)S4125(as)S4246(the)S4406(line)S4594(before)S4889(it.)S5032(Com-)S3576 V1080(ments)S1349(\(starting)S1714(with)S1922(a)S10 B1996(#)S10 R2075(and)S2249(ending)S2551(at)S2653(end)S2827(of)S2940(line\))S3154(have)S3372(an)S3495(indentation)S3975(of)S4087(their)S4300(own)S⌨️ 快捷键说明
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