[Chapter 5] 5.5 Command History

5.5 Command History

Previously executed commands are stored in a history list. The C shell lets you access this list so you can 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. Accessing the history list involves three things:

Making command substitutions (using ! and ^ )
Making argument substitutions (specific words within a command)
Using modifiers to extract or replace parts of a command or word

5.5.1 Command Substitution

`!`	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; execute modified command

5.5.2 Command Substitution Examples

The following command is assumed:

3% vi cprogs/01.c ch002 ch03

Event Number	Command Typed	Command Executed
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`

5.5.3 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.

`:0`	Command name
`:` n	Argument number n
`^`	First argument
`$`	Last argument
`:` n `-` m	Arguments n through m
`-` m	Words 0 through m ; same as `:0-` m
`:` n `-`	Arguments n through next-to-last
`:` n `*`	Arguments n through last; same as n `-$`
`*`	All arguments; same as `^-$` or `1-$`
`#`	Current command line up to this point; fairly useless

5.5.4 Word Substitution Examples

The following command is assumed:

13% cat ch01 ch02 ch03 biblio back

Event Number	Command Typed	Command Executed
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`

5.5.5 History Modifiers

Command and word substitutions can be modified by one or more of these:

5.5.5.1 Printing, Substitution, and Quoting

`: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.

5.5.5.2 Truncation

`:r`	Extract the first available pathname root.
`:gr`	Extract all pathname roots.
`:e`	Extract the first available pathname extension.
`:ge`	Extract all pathname extensions.
`:h`	Extract the first available pathname header.
`:gh`	Extract all pathname headers.
`:t`	Extract the first available pathname tail.
`:gt`	Extract all pathname tails.

5.5.6 History Modifier Examples

From the table in the section "Word Substitution Examples," command number 17 is:

17% cat ch01 ch02 ch03

Event #	Command Typed	Command Executed
19	`!17:s/ch/CH/`	`cat CH01 ch02 ch03`
20	`!: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`
26	`nroff !21:t:p`	`nroff 01.c` (is that want I wanted?)
27	`!!`	`nroff 01.c` (execute it)