Classification of Linux commands
The difference between internal commands and external commands
| External instructions | Internal command |
|---|---|
| Some special instructions integrated in the shell interpreter program are also called built-in instructions | Script file or binary program that can complete specific functions in Linux system |
| Part of the shell | Commands outside the shell interpreter program |
| There is no separate corresponding system file | Each external command corresponds to a file in the system |
| Automatically load into memory and can be used directly | The corresponding file location must be known and can be executed after being loaded by the shell |
Lunux general command line format
[Parameter] Command word [Option] —— (English symbols are case sensitive)
1: [Parameter]
- Command word processing object
- It can be a file name, directory (path) name or user name, etc.
- The number can be zero or more
2: Command word
- Is the most critical part of the entire command
- The only certain command
3: [Options]
- Short format option: use "-" symbol to guide
- Long format option: use'–' symbol to guide
(multiple single character options can be used in combination)
Edit the Linux command line
1: Auxiliary operations for editing Linux command lines
- Tab key: auto-complete
- Backslash'': Force line break
- Ctrl+U key combination: Clear to the beginning of the line
- Ctrl+K key combination: empty to the end of the line
- Ctrl+L key combination: clear screen
- Ctrl+C key combination: cancel this command edit
2: How to get help commands
1: Internal command hellp
- View the help information of the shell internal command
2: The "–hellp" option of the command - Applicable to most Linux external commands
3: Use the man command to read manual pages - Use "↑", "↓" arrow keys to scroll a line of text
- Use Page up and Page Down keys to turn pages
- Press Q or q to exit the reading environment
- Press "/" to find content
View the current working directory-pwd
- Display the user's current working directory location pwd
- Example:
Switch working directory -cd
- Change the user's working directory to another location
| format | Description |
|---|---|
| cd target location | Switch to target location |
| cd ~ or cd | If you do not specify the target location, switch to the current user's home directory |
| cd - | Switch to the directory where you were before the last cd command was executed |
**- Absolute path-full path
- relative path--
- .Current path...the upper level of the current path.../...the upper level of the current path**
The manifestation of the relative path
| Manifestations | Description | Example |
|---|---|---|
| Use directory or file name directly | Represents a subdirectory in the current working directory. File location | grub.conf |
| Start with a period "." | Indicates to start with the current working directory | ./grub.conf |
| Start with two periods "..." | Indicates to use the upper level directory (parent directory) of the current working directory as the starting point | …/vmlinuz |
| Start with "~Username" | Indicates that the home directory of the specified user is used as the starting point | ~teacher |
List the contents of the directory -ls
- displays the contents of the directory, including subdirectories and files related to attribute information
ls [options] [file or directory ...]
-Common options
- -l，-a, -A , -d, -h, -R, --color
-Combining wildcards
- "?": Match an unknown character in the file name
- "*": Match any number of characters in the file name
Set alias-alias
-Simplify commonly used and relatively long commands through the alias mechanism
alias command alias = command
example:
Statistics directory and file space occupation-du
-Count the disk space occupied by the specified directory (or file)
du [Options] [File or directory...]
-Common options
| Options | Description |
|---|---|
| -a | Including all files when counting disk space usage, not just counting directories |
| -h | Has been more user-friendly) (default count in kb, but does not display the unit) shows the statistical results |
| -s | Only the total (Summary) size of the occupied space is counted instead of the size of each subdirectory and file |
Example:
Create a new directory-mkdir
Example:
Common search condition types
| Lookup type | Keyword | Description |
|---|---|---|
| Find by name | -name | Search according to the name of the target file, allowing the use of "*" and "?" wildcards |
| Find by file size | -size | Search according to the size of the target file, generally use the "+""-" sign to set more or less than the specified size as the search condition. Commonly used capacity units include kB (note that k is lowercase), MB, GB |
| Find by file owner | -user | Search based on whether the file belongs to the target user |
| Search by file type | -tye | Search according to the type of file. File types include ordinary files (f), directories (d), block device files (b), character device files (c), etc. |
