Introduction to the Command Line
Sections About All courses
Introduction to the Command Line

Contents

∙ Redirection

Using command outputs to create new files

Sending outputs to files

Move into the folder example_files. We can see, for example, the first three lines of plants.txt with the command

head -3 plants.txt

But what if, instead of printing the output to the terminal, we wanted to put it into a file? This is called “redirecting”, and is done with the character >

head -3 plants.txt > first_three_plants.txt

The terminal will not give you any output, but what is inside the file first_three_plants.txt? Let’s expand on this by using wildcards. Try this command, and examine the contents of the output file:

head -3 * > my_new_file
Warning
Be careful! Redirects will overwrite the target file!! If my_new_file already existed, it would be permanently overwritten by the above command!

Using > will create a new file, or overwrite a file if it already exists. We might want to append instead, and we do that with a double arrow, >>, for example

tail -10 romeo-and-juliet.txt >> another_file
tail -10 king-lear.txt >> another_file

Exercise

Try these redirection and appending tasks, in the folder some_plays.

Exercise
  • Make a new file called “first_50_lines.txt” of the first 50 lines of Romeo and Juliet.
  • Make another new file, containing the last 86 lines, of all the plays.
  • Make a file containing all the lines, from all the plays, containing the word “Queen”.
  • Create a file containing the total number of lines spoken by Theseus, Oberon and Lysander in A Midsummer Night’s Dream.
  • Add the final 100 lines of The Tempest to this file.

Getting help on the command line

Much of your knowledge about commands will of course come from the internet, but you can also look up help and manuals on the command line itself.

man pages

man is short for “manual”. When you run this command, for example

man ls

You will get description and instructions on what the command does, how to use it, and what flags it can take. Some man pages are better than others, but it is good to get familiar with them, and get a feel for how documentation is structured. When you search for a command on the internet, often the best results are just the man pages, presented in a webpage, which might be easier to understand and search through.

Info
  • Note that man pages are presented in a pager: you are not on the command line while viewing man pages.
  • Just like with less, you can leave a man page with q.
Exercise
  • Use man to look up the command wc
  • Use wc, plus a flag, to count the number of lines in Macbeth, in the folder “some_plays”
  • Use wc to count the characters in A Midsummer Night’s Dream.
  • Use wc to count the number of lines in all of the plays in this folder.
  • Use man to look up the following commands. And give the commands themselves a try
history
man
file
cut
sed
echo
tr
du
df
who
w
whoami
Updated on 2022-09-16
Back | Home