The shell is used to accept user commands and pass them to the OS for execution

Basic Navigation and Viewing

pwd

pwd, displays the absolute path of the current directory

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ls

list, lists files in the current directory

Parameters: -l lists attributes of each file, usually aliased as ll

drwxr-xr-x@ 2 fling staff  64  5 24 15:42 test
^ ^  ^  ^ ^ ^   ^     ^     ^   ^ ^  ^     ^
| |  |  | | |   |     |     |   | |  |     |
| |  |  | | |   |     |     |   | |  |     └─ Filename/Directory name (Name)
| |  |  | | |   |     |     |   | |  └─────── Last modification time (Modification Time)
| |  |  | | |   |     |     |   | └────────── Last modification date (day of month) (Day of Month)
| |  |  | | |   |     |     |   └──────────── Last modification month (Month)
| |  |  | | |   |     |     └──────────────── File size (bytes) (Size)
| |  |  | | |   |     └────────────────────── Group (Group)
| |  |  | | |   └──────────────────────────── File owner (Owner)
| |  |  | | └──────────────────────────────── Number of hard links (Number of Hard Links)
| |  |  | └────────────────────────────────── Extended attributes flag (Extended Attributes Flag - @) (macOS specific)
| |  |  └──────────────────────────────────── Others' permissions (Others' Permissions)
| |  └─────────────────────────────────────── Group's permissions (Group's Permissions)
| └────────────────────────────────────────── Owner's permissions (Owner's Permissions)
└──────────────────────────────────────────── File type (File Type)

--- Attribute details:

• File type:
  • -: Regular file (e.g., 1.txt)
  • d: Directory (e.g., test)
  • l: Symbolic link
  • c: Character device file
  • b: Block device file
  • s: Socket file
  • p: Named pipe ---
• File permissions:
  • Divided into three groups, each with three characters, representing permissions for the file owner, group users, and others
  • Each group of characters is rwx representing read, write, and execute permissions; if a permission is missing, use - instead. For concise representation, assign numbers 4\2\1 to r\w\x ---
• Number of hard links:
  • For files, indicates how many filenames point to this file's inode
  • For directories, usually 2 + number of subdirectories. Each directory has . pointing to itself and .. pointing to the parent directory --- -a lists all files, including hidden files . .. .env 1.txt test --- ### cd c, enter a directory

As mentioned earlier, .. represents the parent directory cd - represents entering the previous location

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tree

tree [] displays the structure of directory []

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File and Directory Operations

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touch

touch, touch, update timestamp, but can also create files

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mkdir

mkdir, create directory

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cat

cat, output the contents of a file

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less

less, view a file, can scroll up and down, press q to return Only reads and displays the portion needed for the screen g beginning G end % or p jump by percentage /pattern search forward, ?pattern search backward, n next match, N previous match F continuously monitor new content at the end of the file, similar to tail -f

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more

more, view a file, cannot scroll up, press q to return Loads the entire file into memory at once before displaying

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head

head, output the beginning of a file

head --lines=n file outputs the first n lines of file

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tail

tail, output the end of a file

tail --lines=n file outputs the last n lines of file tail -f continuously view subsequent content

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cp

cp source destination copy files or directories

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mv

mv source destination move, can also be used to rename

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rm

rm, delete rm -r recursive delete, used for directories

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ln

ln, link ln -s source destination symbolic link (soft link), does not store the file, just a shortcut file ln source destination hard link, pointer to the source file, shares the same inode, can be considered a reference, can only point to files

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Permissions and Search

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chmod

Modify permissions u\g\o represents the three group permissions chmod u+x file represents giving the owner execute permission Can also be modified using numbers, e.g., chmod 744 file

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file

file, what file type, e.g., 1.txt: ASCII text

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where/which/whereis

where, find where the file is

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Output, Pipes, and Editing

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echo

echo, output to command line, note that special characters should be wrapped in " "

> redirect standard output to file, e.g., echo "1" > 1.txt >> append to file < redirect standard input from file

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pipe

command1 | command2 | command3 the standard output of one command serves as the standard input of another command

ls -l | grep "*.txt" cat blog.log | grep "ERROR" | less

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nano

Crtl+X exit, Crtl+O save

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vim

In command mode, :wq save and exit, :q! force quit, [n]yy copy n lines, [n]p paste n times to the line below the cursor, dd cut/delete

In command mode, enter i\a\o\I\A\O to enter insert mode; in insert mode, esc enters command mode

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In insert mode, ^ can jump to the beginning of the line, $ jump to the end of the line

In command mode, enter : to enter last-line mode; in last-line mode, esc\enter enters command mode

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Variables and Wildcards

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shell

Define a variable variable=value and it's defined, can be viewed using echo ${variable}, braces are used to prevent ambiguity

Prefix removal, e.g., ff=week01, echo ${ff#week} outputs 01 Remove suffix %

? represents a placeholder for one character, * refers to a placeholder for any characters

--- for i in $(seq 1 10) sequence from 1 to 10 for ((i=0;i<10;i++)) C-style loop

Batch rename

for> do
for> mv ${d} chapter${d#week}
for> done