October 17, 2019

Connecting to the server

Try this using Chrome or Firefox. Microsoft browsers do not work well

Please open the page http://rstudio.iu.edu.tr:4200/

If it works, you will connect to the server from the browser

Create a folder for today’s class

Create a folder called unixstuff and change to that folder

mkdir unixstuff
cd unixstuff


  • Most UNIX commands write to the standard output
    • that is, they write to the terminal screen
  • and many take their input from the standard input
    • that is, they read it from the keyboard
  • There is also the standard error, where processes write their error messages
    • by default, to the terminal screen.

Redirecting the Output

from last class

We use the > symbol to redirect the output of a command. For example, to create a file called list1 containing a list of fruit, type  

$ cat > list1

The cat command reads the standard input (the keyboard) and the > redirects the output, which normally goes to the screen, into a file called list1

To read the contents of the file, type

$ cat list1

Appending to a file

The form >> appends standard output to a file. So to add more items to the file list1, type

$ cat >> list1

Then type in the names of more fruit


(Ctrl-D to stop)

Checking what happened

To read the contents of the file, type

$ cat list1

You should now have two files. One contains six fruit, the other contains four fruit.

Concatenating files

We will now use the cat command to join (concatenate) list1 and list2 into a new file called biglist. Write

$ cat list1 list2 > biglist

What this is doing is reading the contents of list1 and list2 in turn, then outputing the text to the file biglist

See the result

To read the contents of the new file, type

$ cat biglist

Redirecting the Input

We use the < symbol to redirect the input of a command.

The command sort alphabetically or numerically sorts a list. Type

$ sort

Write the names of some animals. Press [Return] after each one.


(control d to stop)

Output of sort

The output will be


Replacing the keyboard by a file

Using < you can redirect the input to come from a file rather than the keyboard. For example, to sort the list of fruit, type

$ sort < biglist

and the sorted list will be output to the screen.

To output the sorted list to a file, type,

$ sort < biglist > slist

Use cat to read the contents of the file slist


To see who is on the system with you, type

$ who

One method to get a sorted list of names is to type,

$ who > names.txt
$ sort < names.txt

This is a bit slow and you have to remember to remove the temporary file names.txt when you have finished

There is a better way

What you really want to do is connect the output of the who command directly to the input of the sort command

This is exactly what pipes do

The symbol for a pipe is the vertical bar |


For example, typing

$ who | sort

will give the same result as above, but quicker and cleaner.

To find out how many users are logged on, type

$ who | wc -l


Using pipes, display all lines of list1 and list2 containing the letter ‘p’, and sort the result.


Command Meaning
command > file redirect standard output to a file
command >> file append standard output to a file
command < file redirect standard input from a file
command1 | command2 pipe the output of command1 to the input of command2
cat file1 file2 > file0 concatenate file1 and file2 to file0
sort sort data
who list users currently logged in