A Survival Guide To Unix Part I

sources and references
1: LINUX®ESSENTIALS, Second Edition by Christine Bresnahan and Richard Blum

2: CS160A, City College of San Francisco

3: https://linuxhint.com/bash_wildcard_tutorial/

4: my own experiences

Table of Contents:

I. Introduction

II. So Why Unix Command Line

III. Common Commands

  1. mkdir
  2. cd
  3. vm_stat
  4. echo $PATH
  5. cal -y
  6. man
  7. touch
  8. ls
  9. cat
  10. who
  11. rm
  12. cp
  13. mv
  14. wildcard
  15. wc
  16. receiving and writing information
  17. multiple commands in one line
  18. sort
  19. echo
  20. cut

I. Introduction

I have been using Unix Command Line for a while now and I can not stop talking about how useful they are. It saves me so much time not have to touch my mouse and get lost in my Finder.

Let's not watse time.

This tutorial is a collection of what I think are useful linux commands that no matter how comfortable you are with your Mac, you still can use them.

This tutorial assumes you run the command lines in a Mac terminal.

II. So Why Unix Command Line

it is so much faster. It is quicker to write a couple letters or commands and click enter then just look through all menu options.

That single reason is good enough for us to learn them.

III. Common Commands

to start:

  1. Launch your terminal in Mac.

  2. Create a working directory for this tutorial: please follow the steps for now, I will explain later. \ In your terminal, type:

    $mkdir unix_tutorial
    $cd unix_tutorial

mkdir

stands for make directory \ mkdir [name_directory] create a directory names name_directory if it does not exist

cd

stands for change directory. \ cd [name_directory] changes the current working directory to name_directory

$mkdir unix_tutorial   
$cd unix_tutorial

what we did above were: first: we create a directory name unix_tutorial \ second: we change the working directory to unix_tutorial. \ Some extra tips on cd command \ to go back to the previous directory, do:

$ cd ..

to go back to the home directory, do:

$ cd ~

Yay! We have set up our work space. Up next, in your terminal, type: vm_stat

unix_tutorial xingvoong$ vm_stat

explanation: unix_tutorial is our working directory\ xing_voong is my user name on my personal laptop\ $ the dollar sign is the start of a unix command \ vm_stat is a unix command

vm_stat

Mach Virtual Memory Statistics: (page size of 4096 bytes)
Pages free:                               41457.
Pages active:                           1746982.
Pages inactive:                         1736050.
Pages speculative:                         9597.
Pages throttled:                              0.
Pages wired down:                        509005.
Pages purgeable:                         102050.
"Translation faults":                  85023185.
Pages copy-on-write:                    3372555.
Pages zero filled:                     47523657.
Pages reactivated:                      1451823.
Pages purged:                            822338.
File-backed pages:                       623825.
Anonymous pages:                        2868804.
Pages stored in compressor:              379743.
Pages occupied by compressor:            151040.
Decompressions:                          189312.
Compressions:                            969158.
Pageins:                                2166764.
Pageouts:                                 25776.
Swapins:                                   2560.
Swapouts:                                  2560.

vm_stat stands for virtual memory statistics. \ vm_stat display information about CPU memory and lock I/O

echo $PATH

unix_tutorial xingvoong$ echo $PATH
~/mongodb-macos-x86_64-enterprise-4.4.0/bin:/Users/xingvoong/.gem/ruby/2.6.0/bin:/usr/local/opt/ruby/bin:/usr/local/opt/ruby/bin:/Library/Frameworks/Python.framework/Versions/3.6/bin:/anaconda/bin:/bin:/sbin:Users/bin:/Users/local/sbin:/Users/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin:/Applications/VMware Fusion.app/Contents/Public:/opt/X11/bin

$PATH is an environment variable. echo $PATH displays the enviroment variable that you are currently on.

cal -y

unix_tutorial xingvoong$ cal -y
                          2021
                          ...
    April                  May                   June          
Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa  Su Mo Tu We Th Fr Sa  
             1  2  3                     1         1  2  3  4  5  
 4  5  6  7  8  9 10   2  3  4  5  6  7  8   6  7  8  9 10 11 12  
11 12 13 14 15 16 17   9 10 11 12 13 14 15  13 14 15 16 17 18 19  
18 19 20 21 22 23 24  16 17 18 19 20 21 22  20 21 22 23 24 25 26  
25 26 27 28 29 30     23 24 25 26 27 28 29  27 28 29 30           
                      30 31 
                          ... 

cal -y shows the current year calendar For each command in unix, there are many options. Options are represented by dash a "-". In the above command, -y mean to choose the year option.

man

To get more information and options for a command, use man.\ Exp:

$ man vm_stat 

to exit out terminal after using man command: control + Z

touch

create a file by touching it

$ touch a_file.txt

or we can create a file using:

> a_file.txt

explanation: the command means that an arrow points to a_file.txt. If a_file.txt already existed, > a_file.txt will clear all the content in it.

in your favorite editor, open a_file.txt, type: "hello, this is a file I use to learn unix"

ls

stands for list. It lists all the files and directories in the current environment variable.

$ ls
a_file.txt

there is only one file in our current working directory

cat

stands for concatenate. It allows us to: 1: view content of a file

$ cat a_file.txt
hello, this is a file I use to learn unix.

the downside of this cat command is when a file contains so much content, there would be too much to display. To overcome that, we could use

$ more a_file.txt

2: concatenate two files:

$ touch file2.txt

create a second file for concatenating \ in your editor, open file2.txt, type "this is a second file" \ to concatenate a_file and file2, do:

$ cat a_file.txt file2.txt
  hello, this is a file I use to learn unix.
this is a second fileXings-MacBook-Pro:unix_tutorial xingvoong$

Since I did not have a new line at the end of file2.txt The outputs are not that pretty. Go back to file2.txt to add a new line.

To write the output to a new file, simply do:

$ cat a_file.txt file2.txt > file3.txt

the above command writes the content of a_file.txt and file2.text into file3.text

$ ls
a_file.txt  file2.txt  file3.txt

Now, there are three files in this directory. To view the content of file3.txt

$ cat file3.txt
hello, this is a file I use to learn unix.
this is a second file

who

displays users who recently logged into the computer

unix_tutorial xingvoong$ who
xingvoong console  Jan  9 13:28
xingvoong ttys000  Jan  9 13:51
xingvoong ttys001  Jan  9 21:48

yes, it was me the entire time. Noone hacks my computer. I hope no one hacks yours either

rm

to remove a file create some files to remove

$ touch a
$ touch b
$ touch c

Now, we will remove them:

$ rm a

remove file a from the current directory

$ rm b c

remove file a and file b from the current directory

create a directory to remove

$ mkdir to_remove
$ rm to_remove
rm: to_remove: is a directory

since to_remove is a directory, we can not remove it using to rm. To remove a directory and files in that directory, we do:

$ rm -r to_remove

-r means recursive

Now, our working directory look likes this:

unix_tutorial xingvoong$ ls
a_file.txt  file2.txt  file3.txt

cp

copy file_a to file_b create file_a.txt with content: "this is file a" \ create file_b.txt with content "this is file b"

$ cp file_a.txt file_b.txt
$ cat file_b.txt
this is file a

Now, the content in file a is also the content in file b

mv

mv file_a to file_b \ first, change the content in file_b.txt back to "this is file b"

$ mv file_a.txt file_b.txt
$ ls
a_file.txt  file2.txt  file3.txt  file_b.txt

After moving file_a.txt to file_b.txt, file_a.txt is deleted

$ mv file_b.txt c.txt
$ ls
a_file.txt  c.txt  file2.txt  file3.txt

After moving file_b.txt to c.txt, file_b.txt is deleted and file c.txt is created

wildcard

this section along deserves it whole stands along tutorial.

Usage:

  • define a pattern for searching
  • group multi files and directories

There are three main wildcard characters:

  • star *
    • searches for a specific character one or more time
  • square bracket []
    • acts similarly to a list argument in python,
    • search for a range or a group of character in the bracket.
  • question mark ?
    • finds fixed number of character where the question mark will specifiy the number of character

Example 1: star

$ ls f*
$ file2.txt  file3.txt

the command ls f*list all the files that start with f. f* mean one or more f

In the current directory, create some more files.

$ touch a b c
$ ls
a  b  c.txt  file3.txt
a_file.txt  c  file2.txt

List all file with a given extensions, such as .txt

$ ls *.txt
a_file.txt  c.txt  file2.txt  file3.txt

Example 2: bracket Lists all file that contains character within a to z

$ ls [a-z]
a  b  c

Lists all file that contains character within a to z and with any extension

$ ls [a-z]*.*
a_file.txt  c.txt  file2.txt  file3.txt

Example 3: question mark I want to search for files with 1 character in name

$ ls ?
a  b  c

Searches for files with 5 characters in name and end with .txt entension

$ ls ?????.txt
file2.txt  file3.txt

wc

$ wc file3.txt
2  15  64 file3.txt

the command above displays 4 fields of information:

  1. number of line
  2. number of words
  3. number of characters
  4. the name of the file

In fact, you can get an individual field by specifing an option.

$ wc -l file3.txt
2 file3.txt

$ wc -w file3.txt
15 file3.txt

$ wc -c file3.txt
64 file3.txt

receiving and writing information

This part is about the commands and characters that we have already seen but now we combine them for different usages.

receiving: a command line receives information, what does this mean?

$ ls *.txt
a_file.txt  c.txt  file2.txt  file3.txt

In here, the information is the start character. What if I do not want to display the result of $ ls *.txt in my terminal but another file called output.txt? We can do:

$ ls *.txt > output.txt

the > character redirects the output of ls *.txt to output.txt

Now if we list all the file, we can see that output.txt is created

$ ls
a  b  c.txt  file3.txt
a_file.txt  c  file2.txt  output.txt

Let's see what inside output.txt, we should expect that it contains the output of command line ls

$ cat output.txt
a_file.txt
c.txt
file2.txt
file3.txt

multiple commands in one line

We can do multiple command in one line to save time or to achieve a result that one command line alone can not do. Yes, we are increasing the level of complexity.

$ mkdir mul; cd mul

In the above command, we created a directory called mul. Right after that, we change our current directory to mul. Two commands are seperated by semi colon ";"

Now, we are in mul . We want to get back to the previous directory aka unix_tutorial by simply do $ cd .. In unix_tutorial directory do:

$ ls | wc -l
9 

Let's break it down, ls lists all the files and directories in the current working directory. wc -l counts that result.

sort

create a file name letters.txt with content: a \ c \ e \ b \ d

$ cat letters.txt
a
c
e
b
d

to sort the content of letters.txt file, we can do

$ sort letters.txt
a
b
c
d
e

the sort commands will not change the content letters.txt. So save the result, we can do something that we have seen above.

sort letters.txt > sorted_letter.txt

to sort in descending order, we can do

$ sort -r letters.txt
e
d
c
b
a

r: reverse option

echo

display in terminal the information that given to the command.

$ echo hello
hello

cut

$ ls | cut -c1
a
a
b
c
c
f
f
l
m
o
s

As we always do, let's break it down. -c1 specifies column 1 option. So the above command first list all the files and directories. Then cut them by their first column. In this case, the first column is the first letter of their names.

echo "a,b"  | cut -d, -f2
b

-d indicates a delimiter. In the above example, the delimiter is comma ", " -f2 means field number 2 to return field number 1, we do

echo "a,b"  | cut -d, -f2
a

to be continued ...

Article By Xing Voong

Xing is a writer and an aspiring software developer. He writes about education, culture, and technology.

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