Shell command-line operations

1.1 Shell prompt

[Email protected] ~]$

If the last character is "#", it indicates that the current Terminal session has Superuser privileges. This permission can be obtained by logging in with the root user or using a terminal that provides superuser privileges.

The prompt is defined by an environment variable named PS1 (Prompt string 1).

1.2 Auto-Completing

Auto-completion can be applied to path names, variables (words starting with $), user names (beginning with ~), commands (the first word at the command line), host names (words begin with @, only valid for host names under/etc/hosts)

Command	Role
alt-$	Displays all possible items. Equivalent to pressing TAB two times
alt-*	Insert all possible matches

1.2 Command line History

The history command outputs a historical record, which defaults to 500.

History commands

Command	Role
Ctrl-p	Move to previous history, equal up Arrow
Ctrl-n	Move to the next history, equal to the down arrow
alt-<	Move to the beginning of the history record
Alt->	Move to the end of the history, which is the current command line
Alt-p	Non-incremental search. Enter search string and type Enter to start search
Alt-n	Forward non-Incremental search
Ctrl-o	Executes the history item and jumps to the next item after execution. Used to perform a series of historical records
Ctrl-r	Reverse incremental search history; Find next match when searching
Ctrl-j	Copy the search content to the current command line (press the left and RIGHT arrow keys to copy, and press ENTER to execute the command immediately)
Ctrl-g or C	Exit Search
!!	Repeat the last command, equivalent to the UP ARROW +enter
!number	command to execute history number line
! String	Executes the most recent history that begins with a string
!? String	Executes the most recent history that contains a string

1.3 Copy and paste

* You can't use ctrl-c and ctrl-v.

Copy	Paste
left mouse button to select text (or double-click to select Word)	Middle mouse button
Ctrl-shift-c	Ctrl-shift-v
Ctrl-insert	Shift-insert

1.4 Virtual Terminal

CTRL-ALT-F1 ~ F6: Switch to 1~6 virtual terminal by the graphical desktop system

ALT-F1 ~ F6: Switch between virtual terminals 1~6

Alt-f7: Back to the graphical desktop system by the virtual terminal

1.5 wildcard characters

Called wildcards or globbing to match a set of file names. Can be used with any command that uses a file name to make arguments.

Note: Use the character range notation sparingly [a-z][a-z]

Wildcard characters	Matching items
*	Matches any number of characters (contains 0)
?	Match any one character (0 not included)
[Characters]	Match any character within a character set
[!characters]	Match any character that is not in character set
[[: Class:]]	Match any character within an in-class character

Character class	Description
[: Alnum:]	Alphabet Set or number set
[: Alpha:]	Alphabet Set
[:d Igit:]	Number Set
[: Lower:]	Small Letter Set
[: Upper:]	Caps set

1.6 Redirects

Linux provides standard input "0", Standard output "1", standard error "2".

">": Redirect the standard output to a file, emptying the original file contents first

Use "> filename" to delete the contents of a file

"<": Read the contents of the file as a standard input command

">>": Redirect standard output to a file, using append mode

"|" : pipe, the standard output of the previous command as standard input for the next command

Simultaneous redirection of standard output and standard errors:

Command > File 2>&1

or new bash-supported command &> file

The redirection of standard errors occurs after standard output redirection, so command 2>&1 >file is wrong.

Ignore output: Redirect output or standard error to file/dev/null.

Ignore all output: command >/dev/null 2>&1

Ignore error: Command 2>/dev/null

1.7 Extensions

Each time the shell command executes, it will be expanded (expansion). Echo makes it easy to verify the extended results. These extensions include:

Path name extension (wildcard characters are used)

Wavy line Extension (~ or ~user, extended to User's home directory)

Arithmetic extension, $ (expression), note all integer operations, support four and take remainder "%", take power "* *", ignore spaces

Curly brace Extension

$ echo {1..5} Output 1 2 3 4 5

$ echo {G... A} output G F E D C B A

$ echo {a{1, 2}, B{3, 4}} output A1 A2 B3 B4

Parameter extensions, such as $path parameters

Command substitution, such as $ (LS) or ' ls '

1.8 References

References can avoid shell extensions. References a strong reference that contains both a weak reference and a single quotation mark.

Weak references: Some special characters lose special meaning, keep the dollar sign "$", backslash "\", anti-quote "'". Therefore, word separation, pathname expansion, wavy line expansion, and braces extension are invalidated. Parameter expansion, arithmetic expansion, and command substitution are still valid.

Strong reference: Suppresses all extensions.

Escape character "\": Output "$", "\", "" "or output escape character" \ n "in a weak reference. Eliminate the meaning of the shell special characters on the command line, such as "$", "!", "&", Spaces

1.9 Shell shortcut key cursor movement

Key combinations	Role
Ctrl-a	Cursor to beginning of line
Ctrl-e	Cursor to end of line
Ctrl-f	Move forward one character, equivalent to the right arrow
Ctrl-b	Move back one character, equivalent to the left arrow
Alt-f	Move forward one word, navigate to the word
Alt-b	Move back one word and position to the beginning of the letter
Ctrl-l	Clear the screen and move the cursor to the beginning of the line, equivalent to clear

Modify text

Key combinations	Role
Ctrl-d	Remove the character at the cursor
Ctrl-t	The character at the cursor and the preceding character are swapped
Alt-t	The word at the cursor and the previous word swap
Alt-l	lowercase from cursor to Word end
Alt-u	Capitalize from cursor to Word end

Cut (Killing) and paste (yanking)

A buffer in which the clipped content exists as a kill-ring

Key combinations	Role
Ctrl-k	Cut from cursor to end of line
Ctrl-u	Cut from cursor to beginning of line
Alt-d	Cut from cursor to current suffix
Alt-backspace	Cut from cursor to prefix, if already at the beginning, cut one single time before
Ctrl-y	Paste

Shell command-line operations