Linux Common Commands | Zheng Zhaoliang

1 Linux commands for files and directory management

commands	description	commands	description
pwd	Print Working Directory	ls	Lists the files and directories
cd	Change Directory	cat	Display the contents of a file
grep	Global Regular Expression Print	cp	Copy files or directories
touch	Create new empty files	mv	Move files or directories from one location to another.
rm	Remove files	rmdir	Remove Directory

2 How to use

2.1 pwd (Print Working Directory):

Usage: pwd
Description: Prints the current working directory.
Example:
```
$ pwd
/home/user/documents
```

2.2 cd (Change Directory):

Usage: cd [directory]
Description: Changes the current working directory to the specified directory.
Example:
```
$ cd /var/log
```

Some additional examples for using the cd command:

cd ~:
- Description: Changes the current working directory to the user’s home directory.
- Example:
```
$ cd ~
```
  or
```
$ cd
```
cd /:
- Description: Changes the current working directory to the root directory.
- Example:
```
$ cd /
```
cd ..:
- Description: Moves one directory up from the current working directory.
- Example:
```
$ cd ..
```

2.3 grep (Global Regular Expression Print):

Usage: grep [options] pattern [files]
Description: Searches for patterns in files and prints matching lines.
Example:
```
$ grep "error" log.txt
```

2.4 touch:

Usage: touch [filename]
Description: Creates an empty file with the specified filename.
Example:
```
$ touch example.txt
```

2.5 rm (Remove):

Usage: rm [options] [files/directories]
Description: Removes files or directories.
Example:
```
$ rm example.txt
```

2.6 ls (List):

Usage: ls [options] [directory]
Description: Lists files and directories in the current or specified directory.
Example:
```
$ ls
```

Some examples of using the ls command with various options:

ls -a (List All):
- Description: Lists all files and directories, including hidden ones (those starting with a dot).
- Example:
```
$ ls -a
```
ls -l (Long Format):
- Description: Lists files and directories in long format, providing detailed information such as permissions, owner, group, size, and modification time.
- Example:
```
$ ls -l
```
ls -f (File Type):
- Description: Lists files and directories without sorting them. It also disables the implicit -a option.
- Example:
```
$ ls -f
```
ls -r (Reverse Order):
- Description: Lists files and directories in reverse order.
- Example:
```
$ ls -r
```
ls -R (Recursive Listing):
- Description: Lists files and directories recursively, showing the contents of subdirectories as well.
- Example:
```
$ ls -R
```
ls -s (Size):
- Description: Lists files and directories with their sizes in blocks.
- Example:
```
$ ls -s
```
ls -h (Human Readable):
- Description: Lists files and directories with human-readable file sizes (e.g., KB, MB, GB).
- Example:
```
$ ls -h
```
ls -l [filename] (Specific File):
- Description: Provides detailed information for a specific file.
- Example:
```
$ ls -l example.doc
```

2.7 cat (Concatenate):

Usage: cat [file]
Description: Concatenates and displays the contents of the specified file(s).
Example:
```
$ cat example.txt
```

2.8 cp (Copy):

Usage: cp [options] source destination
Description: Copies files or directories from the source to the destination.
Example:
```
$ cp example.txt backup/
```

2.9 mv (Move):

Usage: mv [options] source destination
Description: Moves files or directories from the source to the destination. It can also rename files or directories.
Example:
```
$ mv example.txt new_location/
```

More examples of using the mv command with various options:

mv -i (Interactive):
- Usage: mv -i source destination
- Description: Prompts before overwriting existing files.
- Example:
```
$ mv -i file1.txt file2.txt
```
mv -f (Force):
- Usage: mv -f source destination
- Description: Forces the move, overwriting the destination file if it already exists without prompting. This is dangerous action!
- Example:
```
$ mv -f file1.txt file2.txt
```
mv -v (Verbose):
- Usage: mv -v source destination
- Description: Displays informative messages about the move operation.
- Example:
```
$ mv -v file1.txt file2.txt
```

2.10 rmdir (Remove Directory):

Usage: rmdir [options] directory
Description: Removes the specified empty directory.
Example:
```
$ rmdir directory_name
```

3 Linux commands for disk space operation

commands	description
mount	Attaches a filesystem to the directory tree.
umount	Detaches a filesystem from the directory tree.
df	Displays disk space usage for mounted filesystems.
du	Estimates disk usage for directories and files.
fsck	Checks and repairs filesystem inconsistencies.

4 How to use

Certainly! Here’s a more detailed explanation of how to use each command along with examples:

4.1 mount:

Usage: mount [options] device directory
Description: Mounts a filesystem located on a device (such as a hard drive partition or a network share) to a specified directory in the filesystem hierarchy.
Example:
```
$ sudo mount /dev/sdb1 /mnt/usb
```

4.2 umount:

Usage: umount [options] directory
Description: Unmounts a previously mounted filesystem from the directory tree, ensuring that no processes are using the filesystem.
Example:
```
$ sudo umount /mnt/usb
```

4.3 df:

Usage: df [options] [directory]
Description: Displays information about disk space usage for all mounted filesystems or the filesystem containing the specified directory.
Example:
```
$ df -h
```

4.4 du:

Usage: du [options] [directories/files]
Description: Estimates disk usage for the specified directories and files, showing the total size occupied by each.
Example:
```
$ du -sh /home/user
```

4.5 fsck:

Usage: fsck [options] device
Description: Checks and repairs filesystem inconsistencies on a disk device, ensuring the integrity of the filesystem.
Example:
```
$ sudo fsck /dev/sda1
```