Operating Systems & Administration

[Day 1] 7. Some Basic Commands

D

DITISS Admin

•August 26, 2026•5 min read

Shell Information

```
echo $SHELL
```
: Displays the default shell of your system.

Directory and File Listing

```
ls
```
: Displays the contents of the current directory.
```
ls <path>
```
: Displays the contents of a specified path.
```
ls /
```
: Displays the contents of the root directory.
```
ls /boot
```
: Displays the contents of the boot directory.
```
ls /home/
```
: Displays the contents of the home directory.
```
ls /dev
```
: Displays all device files.
```
ls -R
```
: Displays the entire directory hierarchy recursively, showing all files and sub-directories.
```
ls -a
```
: lists all files including hidden ones (starting with
```
.
```
)
```
ls -A
```
: does the same but excludes
```
.
```
(current directory) and
```
..
```
(parent directory).
```
ls -l
```
:
```
cd
```
: Changes current working directory to
```
home
```
directory.
```
cd~
```
: Same as previous. Changes current directory to
```
home
```
directory.
```
cd Desktop/
```
: Changes the current directory to
```
Desktop
```
.
```
cd dir1
```
: Changes the present working directory to
```
dir1
```
.
```
cd ..
```
: Changes the present working directory to its
```
parent
```
or
```
previous
```
directory.
```
cd -
```
: Changes to previous present working directory.
Note: In every directory, by default two entries are made that are hidden. The first one is
```
.
```
and
```
..
```
,
```
.
```
indicates current directory and
```
..
```
indicates parent directory.

System Information

```
cat /proc/cpuinfo
```
: Displays CPU information stored in the
```
/proc
```
directory.
```
cat /proc/meminfo
```
: Displays memory information stored in the
```
/proc
```
directory.
```
date
```
: Displays the current date and time.
```
date -s
```
: Sets the date and time.
```
man <command>
```
: Displays the manual page for a command (e.g.,
```
man date
```
for the date command).

Calendar

```
cal
```
: Displays the calendar of the current month.
```
cal -y
```
: Displays the calendar for the current year.
```
cal -y <year>
```
: Displays the calendar for a specific year.
```
ncal
```
: An alternative command for displaying calendars.

File and Directory Operations

Working Directory

```
pwd
```
: Displays the present working directory.

Creating Directories

```
mkdir <directory>
```
: Creates a directory with the specified name.
- Example:
```
mkdir ditiss
```
```
mkdir <dir1> <dir2> <dir3>
```
: Creates multiple directories.
- Example:
```
mkdir dir1 dir2 dir3
```
```
mkdir -p d1/d2/d3
```
: Creates nested directories in one command.
- Example:
```
mkdir -p d1/d2/d3
```

Clearing Terminal

```
clr
```
: Clears the terminal.
Shortcut:
```
Ctrl + L
```

Removing Directories

```
rmdir <directory>
```
: Removes an empty directory.
- Example:
```
rmdir dir1
```
```
rm -r <directory>
```
: Removes a directory and its contents recursively.
- Example:
```
rm -r dir2
```

File Operations

```
touch <file>
```
: Creates an empty file.
- Example:
```
touch file.txt
```
```
cat <file>
```
: Displays the contents of the specified file.
- Example:
```
cat file.txt
```
```
cat > <file>
```
: Creates or overwrites a file with content.
- End the input with
```
Ctrl + D
```
  .
```
cat >> <file>
```
: Appends content to an existing file.
```
rm <file>
```
: Removes the specified file.
- Example:
```
rm file.txt
```

Copying and Moving Files

```
cp <source> <destination>
```
: Copies files or directories.
- Example:
```
cp file.txt dir1
```
  (Copies
```
file.txt
```
  to
```
dir1
```
  )
- ```
cp -r <source> <destination>
```
  : Recursively copies directories.
- Example:
```
cp -r dir1 dir2
```
  (Copies
```
dir1
```
  to
```
dir2
```
  )
```
mv <source> <destination>
```
: Moves or renames files or directories.
- Example:
```
mv file.txt moved.txt
```
  (Renames
```
file.txt
```
  to
```
moved.txt
```
  )
- Example:
```
mv file.txt dir2
```
  (Moves
```
file.txt
```
  to
```
dir2
```
  ) In this example,
```
dir2
```
  should already be created otherwise this command won't work.

Shortcut Keys

```
Ctrl + L
```
: Clears the terminal.
```
Ctrl + D
```
: Ends input in file creation (
```
cat >
```
or
```
cat >>
```
).

Notes

```
rmdir
```
is only used for removing empty directories.
```
rm -r
```
removes non-empty directories and their contents.
When we use touch command on an existing file, then it updates its time stamp.
While creating a file, if you include a dot (.) before the file name then the file will be hidden. Same for directories as well.

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