| Previously executed commands are stored in a history list. You can access this list to verify commands, repeat them, or execute modified versions of them. The history built-in command displays the history list; the predefined variables histchars, history, and savehist also affect the history mechanism. There are a number of ways to use the history list: Rerun a previous command Edit a previous command Make command substitutions Make argument substitutions (replace specific words in a command) Extract or replace parts of a command or word
The easiest way to take advantage of the command history is to use the arrow keys to move around in the history, select the command you want, and then rerun it or use the editing features described in the section "Command-Line Editing," later in this chapter, to modify the command. The arrow keys are: Key | Description |
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Up arrow ( ) | Previous command. | Down arrow ( ) | Next command. | Left arrow ( ) | Move left in command line. | Right arrow ( ) | Move right in command line. |
The next sections describe some tools for editing and rerunning commands. With the C shell, which does not have the command-line editing features of tcsh , these features are important for rerunning commands. With tcsh, they are less often used, but they still work. 5.6.1. Command Substitution Command | Description |
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! | Begin a history substitution. | !! | Previous command. | !N | Command number N in history list. | !-N | N th command back from current command. | !string | Most recent command that starts with string. | !?string? | Most recent command that contains string. | !?string?% | Most recent command argument that contains string. | !$ | Last argument of previous command. | !!string | Previous command, then append string. | !N string | Command N, then append string. | !{s1}s2 | Most recent command starting with string s1, then append string s2. | ^old^new^ | Quick substitution; change string old to new in previous command, and execute modified command. |
5.6.2. Command Substitution Examples The following command is assumed: 3% vi cprogs/01.c ch002 ch03
Event number | Command typed | Command executed |
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4 | ^00^0 | vi cprogs/01.c ch02 ch03 | 5 | nroff !* | nroff cprogs/01.c ch02 ch03 | 6 | nroff !$ | nroff ch03 | 7 | !vi | vi cprogs/01.c ch02 ch03 | 8 | !6 | nroff ch03 | 9 | !?01 | vi cprogs/01.c ch02 ch03 | 10 | !{nr}.new | nroff ch03.new | 11 | !!|lp | nroff ch03.new | lp | 12 | more !?pr?% | more cprogs/01.c |
5.6.3. Word Substitution Word specifiers allow you to retrieve individual words from previous command lines. Colons may precede any word specifier. After an event number, colons are optional unless shown here. Specifier | Description |
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:0 | Command name. | :n | Argument number n. | ^ | First argument. | $ | Last argument. | % | Argument matched by a !?string? search. | :n-m | Arguments n through m. | -m | Words 0 through m; same as :0-m. | :n- | Arguments n through next-to-last. | :n* | Arguments n through last; same as n-$. | * | All arguments; same as ^-$ or 1-$. | # | Current command line up to this point; fairly useless. |
5.6.4. Word Substitution Examples The following command is assumed: 13% cat ch01 ch02 ch03 biblio back
Event number | Command typed | Command executed |
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14 | ls !13^ | ls ch01 | 15 | sort !13:* | sort ch01 ch02 ch03 biblio back | 16 | lp !cat:3* | lp ch03 biblio back | 17 | !cat:0 3 | cat ch01 ch02 ch03 | 18 | vi !-5:4 | vi biblio |
5.6.5. History Modifiers Command and word substitutions can be modified by one or more of the following modifiers. 5.6.5.1. Printing, substitution, and quoting Modifier | Description |
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:p | Display command, but don't execute. | :s/old/new | Substitute string new for old, first instance only. | :gs/old/new | Substitute string new for old, all instances. | :& | Repeat previous substitution (:s or ^ command), first instance only. | :g& | Repeat previous substitution, all instances. | :q | Quote a word list. | :x | Quote separate words. |
5.6.5.2. Truncation Modifier | Description |
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:r | Extract the first available pathname root (the portion before the last period). | :gr | Extract all pathname roots. | :e | Extract the first available pathname extension (the portion after the last period). | :ge | Extract all pathname extensions. | :h | Extract the first available pathname header (the portion before the last slash). | :gh | Extract all pathname headers. | :t | Extract the first available pathname tail (the portion after the last slash). | :gt | Extract all pathname tails. | :u | Make first lowercase letter uppercase. | :l | Make first uppercase letter lowercase. | :a | Apply modifier(s) following a as many times as possible to a word. If used with g, a is applied to all words. |
5.6.6. History Modifier Examples From the table in the section "Word Substitution Examples," command number 17 is: 17% cat ch01 ch02 ch03
Event number | Command typed | Command executed |
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19 | !17:s/ch/CH/ | cat CH01 ch02 ch03 | 20 | !17:g& | cat CH01 CH02 CH03 | 21 | !more:p | more cprogs/01.c (displayed only) | 22 | cd !$:h | cd cprogs | 23 | vi !mo:$:t | vi 01.c | 24 | grep stdio !$ | grep stdio 01.c | 25 | ^stdio^include stdio^:q | grep "include stdio" 01.c (quotes not shown intcsh output) | 26 | nroff !21:t:p | nroff 01.c (is that what I wanted?) | 27 | !! | nroff 01.c (execute it) |
5.6.7. Special Aliases Certain special aliases can be set in tcsh. The aliases are initially undefined. Once set, the commands they specify are executed when specific events occur. The following is a list of the special aliases and when they are executed:
beepcmd At beep.
cwdcmd When the current working directory changes.
jobcmd Before running a command or before its state changes. Like postcmd, but does not print built-ins.
helpcommand Invoked by the run-help editor command. See the tcsh manpage for details.
periodic Every few minutes. The exact amount of time is set by the tperiod shell variable.
precmd Before printing a new prompt.
postcmd Before running a command.
shell program If a script does not specify a shell, interpret it with program, which should be a full pathname.
5.6.7.1. Examples Demonstrate the cwdcmd alias: [arnold@mybox ~]$ alias cwdcmd 'echo now in $PWD' Set alias [arnold@mybox ~]$ cd /tmp Change directory now in /tmp Output from alias [arnold@mybox /tmp]$ cd Change back home now in /home/arnold Output from alias
Demonstrate the postcmd alias: [arnold@mybox ~]$ alias postcmd 'echo now starting\!' Set alias [arnold@mybox ~]$ ls -FC *.txt Run a command now starting! Output from alias adr.gdb.backcover.txt gdb.backcover.txt sol-d1-2.txt Output from command awkhomepage.txt sol-d1-1.txt
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