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October 17, 2019
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 called unixstuff
and change to that folder
mkdir unixstuff cd unixstuff
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
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
peach grape orange ^D
(Ctrl-D to stop)
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.
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
To read the contents of the new file, type
$ cat biglist
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.
dog cat bird ape ^D
(control d to stop)
sort
The output will be
ape bird cat dog
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
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 |
This class is a derived work from http://www.ee.surrey.ac.uk/Teaching/Unix/
M.Stonebank@surrey.ac.uk, © 9th October 2000
Licensed under a Creative Commons License