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Annotation of 43BSDTahoe/new/help/src/cshell/history, revision 1.1

1.1     ! root        1: .TI CSHELL/HISTORY
        !             2: Reusing Previous Commands and Command Parts [DRAFT]
        !             3: 
        !             4: 
        !             5: History substitution allows you to include special, easily-typed
        !             6: constructs within a command and have the C shell replace them
        !             7: with parts of previous command lines, or events,
        !             8: possibly with small changes.
        !             9: Previous command lines are called events instead of commands
        !            10: in order to emphasize that events contain all the special constructs
        !            11: you entered originally (except history constructs).
        !            12: The history feature makes it easy for you to redo a previous command,
        !            13: to redo a previous command with a correction, and to re-use
        !            14: previous command parts.
        !            15: 
        !            16: Although these interactive applications predominate,
        !            17: there are two non-interactive uses:  defining the arguments to shell
        !            18: aliases and setting the shell's prompt to contain the current event number.
        !            19: To use alias arguments extensively requires the thorough grounding
        !            20: in history subtleties that only a systematic approach can give,
        !            21: and as the mechanisms involved are very complex and not particularly
        !            22: powerful I will postpone a systematic approach until the end.
        !            23: 
        !            24: Setting the shell's prompt is such a special and simple case that I will
        !            25: deal with it now.
        !            26: If you set your prompt (usually "% ") to any string containing !
        !            27: (which you must quote using \\!),
        !            28: the shell will replace the ! with the current event number when it
        !            29: prints the prompt.
        !            30: For instance, to set your prompt to contain the event number
        !            31: followed by a string of your choosing, you might do
        !            32: .IP
        !            33: set prompt = "\\! Command Me O Great One: "
        !            34: .LP
        !            35: Note that ! can only be prevented its special meaning by placing a \\
        !            36: before it; no other kind of quoting will work.
        !            37: 
        !            38: 
        !            39: History for the Lazy Typist
        !            40: 
        !            41: A pre-requisite for gaining access to events (previous command lines)
        !            42: prior to the very last one is to tell the C shell how many events
        !            43: to keep track of.
        !            44: Do this by setting the C shell variable "history" to a
        !            45: number greater than one.
        !            46: Thus the command
        !            47: .IP
        !            48: set history = 20
        !            49: .LP
        !            50: will cause the shell to keep a record of your previous 20 events
        !            51: in an internal list called the history list.
        !            52: You can display the current history list at any time
        !            53: by typing the command "history".
        !            54: If you want to the history list to be saved when you logout,
        !            55: and then be reinstated when you login next,
        !            56: set the variable "savehist" to the same number.
        !            57: To have the these variables set automatically upon logging-in,
        !            58: enter the appropriate commands into your ".cshrc" file.
        !            59: 
        !            60: All history substitutions are triggered on a command line
        !            61: when the user enters special constructs using the
        !            62: characters ! and ^ (circumflex).
        !            63: Whenever the shell makes a history substitution, it always
        !            64: displays the resulting command as you would have entered it
        !            65: without using the history feature.
        !            66: So if the result is other than you expected,
        !            67: you have a chance to interrupt the command before it does harm.
        !            68: 
        !            69: The ^ has only one purpose, and that is to re-do the last command
        !            70: with a correction using a command of the form
        !            71: .IP
        !            72: \fI^oldstring^newstring\fP
        !            73: .LP
        !            74: It works something like the substitute command in the editor,
        !            75: but with the restriction that \fIoldstring\fP
        !            76: be entirely contained in a command word and that none of the
        !            77: special characters significant to the editor have any meaning here.
        !            78: For example,
        !            79: .IP
        !            80: .nf
        !            81: % nroff -ms -Tdtc intro chap1 chap2
        !            82: Cannot open intro
        !            83: % ^tro^troduction
        !            84: nroff -ms -Tdtc introduction chap1 chap2
        !            85: .LP
        !            86: corrects a mistaken file name (the shell printed the resulting command
        !            87: before executing it), but the following fails:
        !            88: .IP
        !            89: .nf
        !            90: % ^o c^oduction c
        !            91: Modifier failed
        !            92: .LP
        !            93: As with the editor, substitutions of this type occur at the
        !            94: first possible point in the command line:
        !            95: .IP
        !            96: .nf
        !            97: % ^ro^roduction
        !            98: nroductionff -ms -Tdtc intro chap1 chap2
        !            99: nroductionff: Command not found.
        !           100: .LP
        !           101: The restrictions on this construct make some kinds of corrections
        !           102: impossible using history.
        !           103: 
        !           104: Another very useful aspect of history is the ability to re-use the
        !           105: last word of the last command using the !$ construct.
        !           106: Typically, a command takes a filename as the last argument,
        !           107: and the next command will likely include the filename again
        !           108: as the last argument, and the next, etc.
        !           109: The command sequence below demonstrates this labor-saving device.
        !           110: .LP
        !           111: .nf
        !           112: .ta 3.5i
        !           113: % vi chapter15.4.new   % myCprogram
        !           114: % spell !$     % vi !$.c
        !           115: spell chapter15.4.new  vi myCprogram.c
        !           116: % nroff -ms !$ > out   % cc !$
        !           117: nroff -ms chapter15.4.new > out        cc myCprogram.c
        !           118: % more !$      % pr !$ | lpr
        !           119: more out       pr myCprogram.c | lpr
        !           120: .LP
        !           121: A previous event (command) can be redone without changes by
        !           122: using the !\fIevent\fP construct, where you replace
        !           123: \fIevent\fP with the first few letters of a previous event.
        !           124: Typically, useful work during a terminal session consists of
        !           125: refining a project with the editor, testing it out, refining some more,
        !           126: then testing some more, etc., and often this means revisiting the same
        !           127: commands time and again.
        !           128: Here is a sample terminal session illustrating how you can take advantage 
        !           129: of such behavior.
        !           130: .LP
        !           131: .nf
        !           132: % more mytext  % !v
        !           133: mytext: No such file or directory      vi mytext
        !           134: % cd confidential      % !s
        !           135: % !mor spell mytext
        !           136: more mytext    % nroff-ms !$ | more
        !           137: mytext: Permission denied      nroff-ms mytext
        !           138: % chmod 644 !$ nroff-ms: Command not found.
        !           139: chmod 644 mytext       % ^ff-^ff -
        !           140: % !m   nroff -ms mytext | more
        !           141: more mytext    % !v
        !           142: % vi !$        vi mytext
        !           143: vi mytext      % !n
        !           144: % spell !$     nroff -ms mytext | more
        !           145: spell mytext   % logout
        !           146: .LP
        !           147: Previous commands may also be specified after ! by using an event
        !           148: number, a numerical offset from the current event, or with the
        !           149: ?\fIstring\fP construct, which finds the last event containing
        !           150: \fIstring\fP not necessarily at the beginning.
        !           151: You can find out event numbers with the "history" command, and
        !           152: just type, say !14, to redo event number 14.
        !           153: A numerical offset such as !-2 will redo the next to last event.
        !           154: As a special case, !! redoes the last event.
        !           155: 
        !           156: Sometimes you want to redo a previous command with one of the
        !           157: above constructs, but only after making a change.
        !           158: This is possible by placing a \fB:s^\fIoldstring\fB^\fInewstring\fR
        !           159: construct after the \fB!\fIevent\fR event specifier.
        !           160: Moreover, the change can be made throughout the event by
        !           161: putting a \fBg\fR before the \fBs\fR.
        !           162: If the history list contained
        !           163: .IP
        !           164: .nf
        !           165: 53 more /usr/man/man1/csh.1
        !           166: 54 readnews -n net.general net.micro net.announce
        !           167: 55 nroff -ms -Tlpr mytext | lpr
        !           168: 56 nroff -ms paper > outfile
        !           169: 57 cp chap1 chap1.old
        !           170: .LP
        !           171: the following commands could exercise these ideas as shown:
        !           172: .IP
        !           173: .nf
        !           174: % !54
        !           175: readnews -n net.general net.micro net.announce
        !           176: % !nro
        !           177: nroff -ms paper > outfile
        !           178: % !?-Tlpr
        !           179: nroff -ms -Tlpr mytext | lpr
        !           180: % !more:s^man1^cat1
        !           181: more /usr/man/cat1/csh.1
        !           182: % !-2:s^mytext^paper
        !           183: nroff -ms -Tlpr paper | lpr
        !           184: % !cp:gs^chap1^chap2
        !           185: cp chap2 chap2.old
        !           186: .LP
        !           187: This concludes the section describing those history features
        !           188: relevant to most normal practices.
        !           189: 
        !           190: 
        !           191: History for Masochists
        !           192: 
        !           193: Any history construct whatever is a special case, very often
        !           194: abbreviated, of the following form for the general history construct:
        !           195: .IP
        !           196: .BI ! event-specifier : word-specifier : modifier : modifier ...
        !           197: 
        !           198: 
        !           199: [to be continued ... jak]

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