Hi everyone, here are the basic UNIX commands that will be useful for the daily usage in the UNIX or Linux operating systems...
1. cd - Change directory
This command will be used very frequently when you're in an UNIX/Linux terminal to change from one directory to another.
Syntax: cd directory_name
cd .. gives directory above the current directory
cd / there is root directory above all directories, which is /, this command will navigate you to that directory.
cd ~ Tilde key refers to the home directory of the current user, this command will navigate one to that directory.
2. pwd - Print working directory
This command will be helpful when you want to know which directory you're currently working in.
Syntax: pwd
3. whoami & who
i.) whoami: Prints the effective user. This command will let you know the current user.
Syntax: whoami
ii.) who: Prints the logged users for the current session.
Syntax: who
4.) ls
This command will list the current directory contents. This is a very useful command.
Syntax: ls: lists directories
ls -a: lists all directories.
5. cat - concatenate command
This command can concatenate the files and print the output on console. It basically can combine contents of files, it can help us view the contents on console.
Syntax: consider we have two files file1 and file2, cat command can be used like this:
cat file1 file2
the combined output will be shown on screen.
One can also view the output of a single file using the command like this:
cat file1
6. clear - clear command
This command helps the user to clear the screen.
Syntax: clear
7. less - less command
Some files may have contents that exceed the screen view, one can use less command and view the contents of a file without missing the content of the file from the screen, clicking enter one can view the contents of the file moving line by line or one can also use up and down arrows on keyboard to view the whole contents of the file.
Syntax: less fileName
8. head - head command
This command helps one to view the first 10 lines of a file by default. One can modify the command to view more or less than 10 lines.
Syntax: head fileName - gives the first 10 lines of the file.
head -20 fileName - gives the first 20 lines of the file.
9. tail - tail command
This command helps one to view the last 10 lines of a file by default. One can modify the command to view more or less than 10 lines.
Syntax: tail fileName - gives the last 10 lines of the file.
tail -20 fileName - gives the last 20 lines of the file.
10. ps - Snapshot of the current processes
This command is very useful, this shows the processes currently running.
Syntax: ps -e : This command shows the process ID (PID) and the process associated with the PID. This command is identical to another command ps -A (shows all processes).
ps -ef : This command shows the user ID (UID), Process ID (PID), start time, and process.
Bonus: chmod - command that changes file permissions.
This command helps one to change file permissions for different users. Users are differentiated as Users, Groups and all others.
Users:
u - users
g - groups
a- all
Permissions:
r - read
w - write
x - execute
one can change the file permissions as follows:
chmod uga+rwx fileName - this command gives read, write and execute permissions to all the users (u,g,a).
chmod u+rw fileName - this command gives read and write permissions to user.
Octal notations for chmod:
r - 4
w - 2
x - 1
One can use the combination of the above permissions adding digits, for example user wants read and write permission, then 4+2 (r+w) gives 6, user wants full permission, then 4+2+1 (r+w+x) gives 7, for example you want to give user full permissions, groups read and write permissions and all others only read permissions, then the command is used like this:
chmod 764 fileName - here first digit is 7 combination of 4+2+1 (r+w+x) for user, 6 combination of 4+2 (r+w) for groups, 4 read permission for all.
Note: All the above commands are case sensitive.
1. cd - Change directory
This command will be used very frequently when you're in an UNIX/Linux terminal to change from one directory to another.
Syntax: cd directory_name
cd .. gives directory above the current directory
cd / there is root directory above all directories, which is /, this command will navigate you to that directory.
cd ~ Tilde key refers to the home directory of the current user, this command will navigate one to that directory.
2. pwd - Print working directory
This command will be helpful when you want to know which directory you're currently working in.
Syntax: pwd
3. whoami & who
i.) whoami: Prints the effective user. This command will let you know the current user.
Syntax: whoami
ii.) who: Prints the logged users for the current session.
Syntax: who
4.) ls
This command will list the current directory contents. This is a very useful command.
Syntax: ls: lists directories
ls -a: lists all directories.
5. cat - concatenate command
This command can concatenate the files and print the output on console. It basically can combine contents of files, it can help us view the contents on console.
Syntax: consider we have two files file1 and file2, cat command can be used like this:
cat file1 file2
the combined output will be shown on screen.
One can also view the output of a single file using the command like this:
cat file1
6. clear - clear command
This command helps the user to clear the screen.
Syntax: clear
7. less - less command
Some files may have contents that exceed the screen view, one can use less command and view the contents of a file without missing the content of the file from the screen, clicking enter one can view the contents of the file moving line by line or one can also use up and down arrows on keyboard to view the whole contents of the file.
Syntax: less fileName
8. head - head command
This command helps one to view the first 10 lines of a file by default. One can modify the command to view more or less than 10 lines.
Syntax: head fileName - gives the first 10 lines of the file.
head -20 fileName - gives the first 20 lines of the file.
9. tail - tail command
This command helps one to view the last 10 lines of a file by default. One can modify the command to view more or less than 10 lines.
Syntax: tail fileName - gives the last 10 lines of the file.
tail -20 fileName - gives the last 20 lines of the file.
10. ps - Snapshot of the current processes
This command is very useful, this shows the processes currently running.
Syntax: ps -e : This command shows the process ID (PID) and the process associated with the PID. This command is identical to another command ps -A (shows all processes).
ps -ef : This command shows the user ID (UID), Process ID (PID), start time, and process.
Bonus: chmod - command that changes file permissions.
This command helps one to change file permissions for different users. Users are differentiated as Users, Groups and all others.
Users:
u - users
g - groups
a- all
Permissions:
r - read
w - write
x - execute
one can change the file permissions as follows:
chmod uga+rwx fileName - this command gives read, write and execute permissions to all the users (u,g,a).
chmod u+rw fileName - this command gives read and write permissions to user.
Octal notations for chmod:
r - 4
w - 2
x - 1
One can use the combination of the above permissions adding digits, for example user wants read and write permission, then 4+2 (r+w) gives 6, user wants full permission, then 4+2+1 (r+w+x) gives 7, for example you want to give user full permissions, groups read and write permissions and all others only read permissions, then the command is used like this:
chmod 764 fileName - here first digit is 7 combination of 4+2+1 (r+w+x) for user, 6 combination of 4+2 (r+w) for groups, 4 read permission for all.
Note: All the above commands are case sensitive.
