Tildes, Pipes and Redirects
A tilde is
~
and pipe is|
The home directory
The symbol ~
stands for your home directory. This is usually /Users/username
on a mac and something like c:\Users\username
on a PC. You can use this to always make sure you’re talking about the right place without typing too much.
cd ~/Desktop
will always take you right to your desktopcd ~/Downloads
will always take you right to your downloads folderatom ~/.bash_profile
will maybe use Atom to open the file named.bash_profile
that is sitting in your home directory
It doesn’t seem that useful when I type it all out but I promise you’ll use it all of the time.
When I say “home” you think “~
”
Redirecting output with >
You can use >
to take the output of a command (or a list of commands) and save it to a file. It’s called redirecting output. It’s nice.
Let’s say we want to find all of the lines in animals.txt
that mention camel
and save it to camels.txt
. First we grep
to display the lines, then we use >
to redirect the output to a file.
grep camel animals.txt > camel.txt
Let’s say our p
key was broken, so we unfortunately could not use the cp
(copy) command. Because we’re practically geniuses, we could use cat
and >
instead. cat
will display the entire file, then >
will save that output into your file (a.k.a. redirect it to the file).
cat animals.txt > animals2.txt
Maybe a cunning yet overly nosy professor wants to know everything you’ve been typing on the command line. The history
command displays your last however-many commands you’ve typed. Maybe he asks you to save your history to a file called history.txt
on your Desktop.
history > ~/Desktop/history.txt
|
- Piping
Piping - using a |
- is taking the output from one command and sending it to another.
Example 1
- We can use
grep dog animals.txt
to see all of the lines inside ofanimals.txt
that contain the textdog
. - We can use
wc -l animals.txt
to count the lines inside ofanimals.txt
But what if we want to find the lines that contain dog
, and then count those lines? Piping, obviously!
grep dog animals.txt | wc -l
Example 2
- We can use
cat names.txt
to view a list of names in thenames.txt
file - We can use
uniq names.txt
to get rid of adjacent lines that are the same - We can use
sort names.txt
to put the names in alphabetical order
Maybe we want to see a list of every name in names.txt
, but no repeats. We can’t just use uniq
, because it only removes repeats next to each other. We need to sort the list of names and then get rid of repeats.
cat names.txt | sort | uniq
You could also just do
sort names.txt | uniq
And if you wanted to see how many times each name appears? You could add the -c
(count) flag to uniq
.
sort names.txt | uniq -c