See this page as a slide show

CS155 Commands1

Review

Command structure	command [option]... [argument]...
Commands	man, pwd, ls, cd
Pathnames	/, ~, ., ..

Notes

• Information on a Unix system is organized in a tree structure known as the file system.
• All files have an absolute path given their location from the file system root, /, or a user's home directory.
• On login, our starting point is called the home directory, represented by ~ or ~username
• We can refer to the current directory with . and the parent directory with ..
• We can navigate the file system using the Unix commands: pwd, ls, cd

Learning More with man and info

Many Unix command have options that modify their behavior.

To learn more about a specific command try:

• man – show manual for command
• info – show info page for command

Consider them travel guides. man and info can answer many of your questions.

Viewing Files

% pwd
/tmp
% ls
my_file1
% cat my_file1
Hi, everybody!
Hi, Dr. Nick!

The simplest way to view the contents of a file is to use:

• more – show a file one screenful at a time
• cat – dump the complete file to the screen

Modifying the file system

% ls
my_file1
% cp my_file1 my_file2
% ls
my_file1  my_file2
% mv my_file1 file1
% ls
file1  my_file2
% rm file1
% ls
my_file2

Here are three commands for handling files:

• cp – copy a file to some location
• mv – move a file to a new location
• rm – remove a file

Modifying the file system (cont.)

% ls
my_file2
% mkdir new_dir
% ls -l
total 8
-rw------- 1 boese fac 4 Jan 19 14:43 my_file2
drwx------ 2 boese fac 4096 Jan 19 14:44 new_dir
% rmdir new_dir
% ls
my_file2

The previous commands allowed us to move files around in the file system, but what about modifying the structure itself?

• mkdir: make directory
• rmdir: remove directory

echo, echo, echo, echo, echo, echo

% echo hey children
hey children
%echo hey         children
hey children
% echo "hey         children"
hey         children
% echo "~"
~
% echo ~
/Users/davematt
%

The echo command prints some text to the screen.

• Use " to preserve text on the command line

Is this useful for anything? Sure!

Redirection

What if we don’t want the output of a command to go to the screen but to a file? Or get the input to a command from a file instead of the keyboard?

Redirection allows us to change where a command gets input or sends output.

• > - redirect output to a new file
• >> - redirect output to an existing file and append to the end
• < - redirects the input to a file (instead of the keyboard)
• | - sends the output of one program to another program

Output redirection

% echo "hello there, children"
hello there, children
% echo "hello there, children" > chef
% ls
chef  my_file2
% cat chef
hello there, children
% echo "hey chef" >> chef
% cat chef
hello there, children
hey chef
% date
Wed Dec 25 16:22:12 MST 2024
% date >chef
% cat chef
Wed Dec 25 16:22:12 MST 2024

• We can use echo to put text into a file.
• You will find this useful for your homework until we get to text editors.

More output redirection

% ls
chef my_file2
% ls >file_list
% ls
chef  file_list  my_file2
% cat file_list
chef
file_list
my_file2
% pwd >> file_list
% cat file_list
chef
file_list
my_file2
/tmp

echo isn’t the only command whose output we can redirect.

Input redirection

% ls -l >tempfile
% more <tempfile
...
% more tempfile
...
%

Many commands accept input from a file or a command line argument.

Output redirection to a program

%ls -l > tempfile
%more tempfile
...
%rm tempfile
% ls -l | more
...
%

This is useful for combining operations without making temporary files

• Try ls -l | more for listing a directory with many files
• Try man bash | more to learn about the command line interpreter

Summary

• To learn more about a command use: man or info
• To view files use: more or cat
• To modify the file system use: cp, mv, rm, mkdir, rmdir
• To send text somewhere use: echo
• To preserve text use: "
• To redirect the output of a command use: >, >>, |
• To redirect the input of a command use: <