Basic commands in Linux

  • Below is the table including the most common commands in Linux operating system
  • These commands are gone through more properly in this section
Utility Description Usage
pwd Print current working directory pwd
cd Change current working directory cd directory
mkdir Create a new directory mkdir directory
mv Rename or move a file or directory mv source target
ls List directory contents ls directory
rm Remove a file or directory rm file (use -r with dirs)
cp Copy a file or directory cp source target

PWD (Print Current Working Directory)

  • pwd command prints the directory path where the command was executed (current working directory)
testuser@ubuntu-PC:~$ pwd
/home/testuser
  • pwd command makes it easier for new users to navigate in Linux file system

  • Important:

    • Executed command will always affect the current working directory if not stated otherwise
    • The default working directory is user's home directory
    • For example, user home directories are located in /home directory by default
    • This means that current working directory for testuser /home/testuser at start

  • Example for the usage of pwd command

testuser@ubuntu-pc:~$ pwd
/home/testuser
testuser@ubuntu-pc:~$ su -
Password:
root@ubuntu-pc:~# pwd
/root
root@ubuntu-pc:~# su – testuser
Password:
testuser@ubuntu-pc:~$ pwd
/home/testuser

LS (List the Contents of a Directory)

  • ls command is used to list the contents of a directory
  • If command is issued without target directory, the current working directory content will be listed
  • Example where current working directory is listed:
testuser@ubuntu-pc:~$ pwd
/home/testuser
testuser@ubuntu-pc:~$ ls
data sensors.txt
  • Figure below presents this directory location

LS command directory example

  • Examples where other directory is provided as an argument for the command

  • List root directory content

testuser@ubuntu-pc:~$ ls /
bin   dev   initrd.img     lib64      mnt   root     snap    sys    var
boot  etc   initrd.img.old lost+found opt   run      srv     tmp    cdrom
home  lib   media          proc       sbin  swap.img usr
  • List user's home directory content
testuser@ubuntu-pc:~$ ls ~
data sensors.txt
  • List the content of /home directory
testuser@ubuntu-pc:~$ ls /home
testuser
  • List the content of both user's home directory as well as /home directory
testuser@ubuntu-pc:~$ ls ~ /home
/home:
testuser

/home/testuser:
data sensors.txt
  • Listing format can be changed with options

  • Examples of different listing formats

  • List using long listing format with file and directory permissions

testuser@ubuntu-pc:~$ ls -l
total 4
drwxrwxr-x   2 testuser testuser 4096 Aug 20 05:20 data
-rw-rw-r--   1 testuser testuser 0    Aug 20 05:20 sensors.txt
  • List also hidden files and directories starting with . character
testuser@ubuntu-pc:~$ ls -a
.bash_history   .bashrc   data    .profile     .sudo_as_admin_successful
.bash_logout    .cache   .gnupg   sensors.txt
  • ls command options can also be combined
  • For example, ls -la command lists directory contents using long listing format and in addition, all hidden files and directories are included in listing
testuser@ubuntu-pc:~$ ls -la /etc/cron.d
total 1
drwxr-xr-x 1 root root 512 Jul 25  2018 .
drwxr-xr-x 1 root root 512 Sep 29 08:13 ..
-rw-r--r-- 1 root root 102 Nov 16  2017 .placeholder
-rw-r--r-- 1 root root 589 Jun 26  2018 mdadm
-rw-r--r-- 1 root root 191 Jul 25  2018 popularity-contest

CD (Change Directory)

  • Moving between directories can be done with cd command (change user's current working directory)

  • Directory path will be given as an argument (either as absolute or relative path)

    • Absolute path will always be formed starting from the system root (/)
    • Relative path will always be formed starting from the current working directory (from the directory where the command was executed)

  • Example: Let's move from user's home directory to /var/log directory

  • Using absolute path:
testuser@ubuntu-pc:~$ cd /var/log
  • Using relative path:
testuser@ubuntu-pc:~$ cd ../../var/log
  • Below is a figure illustrating the location of the source and target directory within the Linux filesystem

CD command example

  • As can be seen from the figure below, with relative path user must first move two directory levels backwards before entering into /var/log directory

  • Important: The absolute path can easily be used from anywhere on Linux file system!

  • cd command arguments are presented in the table below

Argument Description
No argument Changes to user's home directory
~ Changes to user's home directory
.. Moves one step backwards in file system
Path Changes to target path
- Changes to directory where user was before the previous directory change

Touch (Change File Timestamps)

  • touch command is used to create a new file or update the timestamp of an existing file
  • Example where a new file is created under user's home directory
testuser@ubuntu-pc:~$ ls
data sensors.txt
testuser@ubuntu-pc:~$ touch testfile.txt
testuser@ubuntu-pc:~$ ls
data sensors.txt testfile.txt
  • Example where timestamp of an existing file is updated
testuser@ubuntu-pc:~$ ls -la /tmp
drwxrwxrwx  1 root root 512 Dec 10  2019 test.txt
testuser@ubuntu-pc:~$ touch /tmp/test.txt
testuser@ubuntu-pc:~$ ls -la /tmp
drwxrwxrwx  1 root root 512 Sep 30 12:52 test.txt

MKDIR (Make Directory)

  • mkdir command is used to create a new directory
  • Directory name will be provided as an argument for the command
  • Example where data2 directory is created under user's home directory
testuser@ubuntu-pc:~$ ls
data sensors.txt testfile.txt
testuser@ubuntu-pc:~$ mkdir data2
testuser@ubuntu-pc:~$ ls
data data2 sensors.txt testfile.txt
  • -p option can used to create nested directories with same command
  • Example where data3, data4 and data5 directories are created (data5 is a subdirectory of data4 and data4 is a subdirectory of data3)
testuser@ubuntu-pc:~$ ls
data data2 sensors.txt testfile.txt
testuser@ubuntu-pc:~$ mkdir -p data3/data4/data5
testuser@ubuntu-pc:~$ ls data3/data4
data5

CP (Copy File or Directory)

  • cp command is used for copying files and directories from one directory to another
  • Source and destination directories are provided as arguments for the command
  • Example: Let's copy sensors.txt file to data3 directory and give file a new name (sensors_new.txt)

CP command example 1

testuser@ubuntu-pc:~$ cp sensors.txt data3/sensors_new.txt
testuser@ubuntu-pc:~$ ls data3
data4 sensors_new.txt
  • When copying a directory -r (recursive) option must be used
  • Example: Let's copy data4 directory from data3 directory into current working directory (.)

CP command example 2

testuser@ubuntu-pc:~$ ls
data data2 data3 sensors.txt testfile.txt
testuser@ubuntu-pc:~$ cp -r data3/data4 .
testuser@ubuntu-pc:~$ ls
data data2 data3 data4 sensors.txt testfile.txt

MV (Rename and Move Files)

  • Renaming and moving files and directories is done with mv command
  • Similar to cp command, source and destination directories are provided as arguments
  • Example: Let's move sensors.txt file into data4 directory and give destination file a new name (moved_sensors.txt)

MV command example

testuser@ubuntu-pc:~$ ls
data data2 data3 data4 sensors.txt testfile.txt
testuser@ubuntu-pc:~$ mv sensors.txt data4/moved_sensors.txt
testuser@ubuntu-pc:~$ ls
data data2 data3 data4 testfile.txt
testuser@ubuntu-pc:~$ ls data4
data5 moved_sensors.txt
  • Important: When copying source file to destination source will last. When moving source file to destination source file will be removed!

RM (Delete Files and Directories)

  • rm command is used to delete files and directories
  • One or more targets must be provided as arguments for the command
  • Like with cp command, -r option must be used when deleting directories (recursive action)
  • Example: Let's delete data4 directory including all its contents

RM command example

testuser@ubuntu-pc:~$ ls
data data2 data3 data4 testfile.txt
testuser@ubuntu-pc:~$ rm -r data4
testuser@ubuntu-pc:~$ ls
data data2 data3 testfile.txt

Wildcards

  • Wildcards are characters which can be used as filters for commands (cp, mv, rm, ls etc.)
  • Wildcards:
    • * equals zero or more characters
    • ? equals any single character
    • [list] equals any given character included inside the list
  • Below are a few examples of wildcard use
  • The directory contents are presented below
testuser@ubuntu-pc:~$ ls
sensor1.r    sensor2.c    sensor3.log    sensor4.log    server1.log    server2.log
  • Example: Let's list all files ending with .c string
testuser@ubuntu-pc:~$ ls *.c
sensor2.c
  • Example 2: Let's list all sensor files ending with .log string
testuser@ubuntu-pc:~$ ls sensor?.log
sensor3.log    sensor4.log
  • Example 3: Let's list all sensor files ending with c or r characters
testuser@ubuntu-pc:~$ ls sensor?.[cr]
sensor1.r    sensor2.c