tcsh keeps a list of commands you have typed recently.
- Some features are available to help you correct mistakes or save you from typing whole commands repeatedly.
- You can change one string in the previous command to a different string with ^ (caret) characters on the next command line:
% ls
long-file-name
% rm long-flie-name
long-flie-name: No such file or directory
% ^li^il
rm long-file-name
%
- As with all history operations, the shell shows you resulting command line after its editing but you do not get a chance to say whether or not you really want to do the resulting command.
- The general form of substitution is:
% ^from^to^
- The shell will look through the previous command and change the first occurence of from to to.
- Make sure to give enough characters to match what you want and not a set of characters farther to the left in the previous command.
- tcsh uses the history shell variable as the number of commands to save.
- The default value is somewhat small, but can set it with:
% set history = 100
- Set the histdup variable to indicate that duplicate events should not be saved.
- If the first word of the savehist shell variable is a number, then that is the number of commands that will be saved when you log off.
- The second word can be merge if you want current history merged with contents of your ~/.history file.
- The history command shows you commands entered in the history:
% echo $history
100
% set history = 200
% echo $history
200
% history
1 21:37 echo $history
2 21:37 set history = 200
3 21:37 echo $history
4 21:37 history
%
- The first number is the number of the history item, the second number is the time of day it was executed, and the rest of the line is the command.
- Because the command number is sometimes useful, many people make that part of their prompt:
% set prompt = "\! % "
11 % ls
temp
12 %
- If the string making up the prompt has "!" in it, that "!" will be replaced with the number of the command about to be entered.
- The "!" character is used to indicate history substitutions:
- !n gets replaced by the command nin the history listing.
- !-n gets replaced by command nback in the history listing (relative).
- !! gets replaced with the previous command (can be just ! if followed by a word selector described below).
- !string gets replaced by the most recent command beginning with string.
- !?string? gets replaced by the most recent command with string in it, can skip trailing "?" if string is last thing on this command line.
- A quick example of how this might be useful, when programming with a language that needs to be compiled (e.g. C) working involves doing the same basic three things in a loop - edit, compile, test, edit, compile, test, edit, compile, test ...
% vi prog.c
% cc prog.c
% a.out
% !v
vi prog.c
% !c
cc prog.c
% !a
a.out
%
- Any of the history substitutions may be followed by ":" and a word designator, which specifies a word or range of words from the previous command.
- Word designators are:
- :0means first word (command)
- :n means nth argument, so :1means first argument
- :^ same as :1
- :$is last argument no matter what number it is
- :% may be used with !?string?and becomes the argument matched by string
- :x-y gives arguments x through y
- :* is same as :^-$ but returns nothing if there were no arguments (would be an error for :^-$)
- :x* is arguments x through last argument
- If a word designator begins with ^, $, *, %, or - then you can skip the :
- Again, the most common use of this is to reuse the last argument of the previous command:
% more prog.c
% rm !$
rm prog.c
%
- You can grab any argument though:
% ls -l mbox.old mbox
-rw------- 1 csgst00 visitors 402 Mar 3 06:00 mbox
-rw------- 1 csgst00 visitors 1391 Feb 27 15:51 mbox.old
% rm !!:2
rm mbox.old
%
- You can end a history substitution with :pto print the new command line but not execute it.
- This is useful to make a previous command the most recent to make editing it easier.
