plan9.ps

早期freebsd实现

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12 B f
(Rc \320 A Shell for Plan 9 and UNIX Systems)9 2230 1 1765 1230 t
10 I f
(Tom Duff)1 381 1 2689 1470 t
10 R f
(AT&T Bell Laboratories)2 993 1 2383 1650 t
(Murray Hill, New Jersey 07974)4 1267 1 2246 1770 t
10 I f
(ABSTRACT)2643 2150 w
(Rc)1330 2410 w
10 R f
( also runs on a variety of traditional sys-)8 1641( It)1 115( interpreter for Plan 9.)4 900(is a command)2 561 4 1463 2410 t
( provides similar facilities to Bourne's)5 1580( It)1 120( SunOS and the Tenth Edition.)5 1273(tems, including)1 627 4 1080 2530 t
10 I f
(/bin/sh)1080 2650 w
10 R f
( paper intro-)2 497( This)1 229(, with some small additions and mostly less idiosyncratic syntax.)9 2601 3 1353 2650 t
(duces)1080 2770 w
10 I f
(rc)1335 2770 w
10 R f
( why it varies)3 547('s highlights with numerous examples, and discusses its design and)9 2715 2 1418 2770 t
(from Bourne's.)1 610 1 1080 2890 t
10 B f
(1. Introduction)1 670 1 720 3250 t
10 R f
( new)1 208( porting the Bourne shell to an incompatible)7 1875( As)1 177(Plan 9 needs a command-programming language.)5 2060 4 720 3406 t
( new command interpreter, called)4 1350(environment seemed a daunting task, I chose to write a)9 2232 2 720 3526 t
10 I f
(rc)4330 3526 w
10 R f
(because it runs)2 599 1 4441 3526 t
( could hardly resist trying to)5 1220( tinkering with perfection is a dangerous business, I)8 2197(commands. Although)1 903 3 720 3646 t
( Thus)1 250(`improve' on Bourne's design.)3 1226 2 720 3766 t
10 I f
(rc)2221 3766 w
10 R f
(is similar in spirit but different in detail from Bourne's shell.)10 2424 1 2329 3766 t
(The bulk of this paper describes)5 1318 1 720 3922 t
10 I f
(rc)2071 3922 w
10 R f
( features with many small examples and a few larger ones.)10 2426('s principal)1 460 2 2154 3922 t
(We close with a discussion of the principles guiding)8 2143 1 720 4042 t
10 I f
(rc)2895 4042 w
10 R f
( it differs from Bourne's design.)5 1317('s design and why)3 745 2 2978 4042 t
( features, as individual details)4 1198(The descriptive sections include little discussion of the rationale for particular)10 3122 2 720 4162 t
( skip to the discussion at the end before)8 1632( impatient reader may wish to)5 1230( The)1 213(are hard to justify in isolation.)5 1245 4 720 4282 t
(skimming the expository parts of the paper.)6 1740 1 720 4402 t
10 B f
( commands)1 486(2. Simple)1 420 2 720 4642 t
10 R f
(For the simplest uses)3 881 1 720 4798 t
10 I f
(rc)1639 4798 w
10 R f
( all of the following behave as)6 1293( Thus)1 263(has syntax familiar to Bourne-shell users.)5 1724 3 1760 4798 t
(expected:)720 4918 w
9 CW f
(date)1008 5088 w
(con alice)1 486 1 1008 5198 t
(who >user.names)1 810 1 1008 5308 t
(who >>user.names)1 864 1 1008 5418 t
(wc <file)1 432 1 1008 5528 t
(echo [a-f]*.c)1 702 1 1008 5638 t
(who | wc)2 432 1 1008 5748 t
(who; date)1 486 1 1008 5858 t
(cc *.c &)2 432 1 1008 5968 t
(cyntax *.c && cc -g -o cmd *.c)7 1620 1 1008 6078 t
(rm -r junk || echo rm failed!)6 1566 1 1008 6188 t
10 B f
(3. Quotation)1 559 1 720 6488 t
10 R f
(An argument that contains a space or one of)8 1813 1 720 6644 t
10 I f
(rc)2565 6644 w
10 R f
( in apostrophes)2 621('s other syntax characters must be enclosed)6 1771 2 2648 6644 t
(\()720 6764 w
10 CW f
(')753 6764 w
10 R f
(\):)813 6764 w
9 CW f
(rm 'odd file name')3 972 1 1008 6934 t
10 R f
(An apostrophe in a quoted argument must be doubled:)8 2170 1 720 7114 t
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10 R f
(- 2 -)2 166 1 2797 480 t
9 CW f
(echo 'How''s your father?')3 1404 1 1008 830 t
10 B f
(4. Variables)1 536 1 720 1130 t
10 I f
(Rc)720 1286 w
10 R f
( by typing, for)3 602( may be given values)4 879( Variables)1 441(provides variables whose values are lists of arguments.)7 2259 4 859 1286 t
(example:)720 1406 w
9 CW f
(path=\(. /bin /usr/bin\))2 1188 1 1008 1576 t
(user=td)1008 1686 w
(tty=/dev/tty8)1008 1796 w
10 R f
(The parentheses indicate that the value assigned to)7 2049 1 720 1976 t
10 CW f
(path)2798 1976 w
10 R f
( strings. The variables)3 897(is a list of three)4 632 2 3067 1976 t
10 CW f
(user)4626 1976 w
10 R f
(and)4896 1976 w
10 CW f
(tty)720 2096 w
10 R f
(are assigned lists containing a single string.)6 1735 1 925 2096 t
(The value of a variable can be substituted into a command by preceding its name with a)16 3505 1 720 2252 t
10 CW f
($)4250 2252 w
10 R f
(, like this:)2 398 1 4310 2252 t
9 CW f
(echo $path)1 540 1 1008 2422 t
10 R f
(If)720 2602 w
10 CW f
(path)811 2602 w
10 R f
(had been set as above, this would be equivalent to)9 1997 1 1076 2602 t
9 CW f
(echo . /bin /usr/bin)3 1080 1 1008 2772 t
10 R f
(Variables may be subscripted by numbers or lists of numbers, like this:)11 2842 1 720 2952 t
9 CW f
(echo $path\(2\))1 702 1 1008 3122 t
(echo $path\(3 2 1\))3 918 1 1008 3232 t
10 R f
(These are equivalent to)3 928 1 720 3412 t
9 CW f
(echo /bin)1 486 1 1008 3582 t
(echo /usr/bin /bin .)3 1080 1 1008 3692 t
10 R f
( the subscript)2 555( Otherwise,)1 496(There can be no space separating the variable's name from the left parenthesis.)12 3269 3 720 3872 t
(would be considered a separate parenthesized list.)6 1992 1 720 3992 t
(The number of strings in a variable can be determined by the)11 2431 1 720 4148 t
10 CW f
($#)3176 4148 w
10 R f
( example,)1 388(operator. For)1 546 2 3321 4148 t
9 CW f
(echo $#path)1 594 1 1008 4318 t
10 R f
(would print the number of entries in)6 1443 1 720 4498 t
10 CW f
($path)2188 4498 w
10 R f
(.)2488 4498 w
(The following two assignments are subtly different:)6 2070 1 720 4654 t
9 CW f
(empty=\(\))1008 4824 w
(null='')1008 4934 w
10 R f
(The first sets)2 538 1 720 5114 t
10 CW f
(empty)1294 5114 w
10 R f
( second sets)2 501( The)1 217( list containing no strings.)4 1085(to a)1 158 4 1630 5114 t
10 CW f
(null)3628 5114 w
10 R f
(to a list containing a single)5 1135 1 3905 5114 t
(string, but the string contains no characters.)6 1742 1 720 5234 t
( indistinguishable\),)1 775(Although these may seem like more or less the same thing \(in Bourne's shell, they are)15 3545 2 720 5390 t
( other things)2 500( Among)1 350(they behave differently in almost all circumstances.)6 2060 3 720 5510 t
9 CW f
(echo $#empty)1 648 1 1008 5680 t
10 R f
(prints 0, whereas)2 679 1 720 5860 t
9 CW f
(echo $#null)1 594 1 1008 6030 t
10 R f
(prints 1.)1 328 1 720 6210 t
(All variables that have never been set have the value)9 2097 1 720 6366 t
10 CW f
(\(\))2842 6366 w
10 R f
(.)2962 6366 w
10 B f
(5. Arguments)1 602 1 720 6606 t
10 R f
(When)720 6762 w
10 I f
(rc)983 6762 w
10 R f
( from a file, the file has access to the arguments supplied on)12 2405(is reading its input)3 742 2 1091 6762 t
10 I f
(rc)4264 6762 w
10 R f
('s command line.)2 693 1 4347 6762 t
(The variable)1 504 1 720 6882 t
10 CW f
($*)1252 6882 w
10 R f
( names)1 282( The)1 207( it.)1 108(initially has the list of arguments assigned to)7 1807 4 1400 6882 t
10 CW f
($1)3831 6882 w
10 R f
(,)3951 6882 w
10 CW f
($2)4003 6882 w
10 R f
(, etc. are synonyms for)4 917 1 4123 6882 t
10 CW f