Linux Command Line

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1 - Hello Bash Scripting

What this command does is shows all the available shells on system. Any can be used.

Shows path of bash. Add this to any script that is written

In order to make script executable, have to add chmod +x to it.

./ in front to run script

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2 - Redirect to file

Show how to capture output and then send it to a file. 

When ran, creates a file called file.txt

Script becomes an editor. Whatever is written when script is executed

In order to come out of it, you have to press Ctrl + D.

Output of one displays output of another. Essentially replaces text.

In order to append, put 2 >>

3 - comments

Has no value except explaining code to programmer.

Doesn't show in execution of code. If there are 500 lines of code it does not make to out # on each individual line

:'

' to multi line comment

Heredoc delimeter

Similar to the variable like

4 - Conditional statements

Inside if condition, checks that count equals 10. Since condition is true, execute the block.

No output, since no else block and program doesn’t know what to do.

AND Operator

Checks if age is greater than 18 and less than 40

Both conditions have to be true

One true condition, one false condition

-o for OR operator . -o can also be substituted with ||

5 - Loops

While:

For:

6 - Script Input

 Input represents $1, $2, $3

Create an array with unknown number of inputs

Prints all the values that are taken in.

Prints length of array as well

6 Script Input

7 Script Output

1 file for standard output and 1 file for standard error

8 Sending Output

Output from one script is being sent to another

9 Strings Processing

Compares 2 inputs to see if they match

10 Numbers and Arithmetic

To add numbers:

Or can use expression

11 Declare Command

Bash does not have a strong type system. Cannot restrict variables, however you can use attributes set by a command. Declare is a bash built in command that allows you to update attributes applied to variables within scope of shell.

Declare -p shows ALL variables

Can see that it is trying to print out twice. This is because pwd file is being declared as a read variable

12 Arrays

Prints out all of the arrays

13 Functions

In order to make functions work, they need to be called

14 Files and Directories

Learn how to create directories/check if current directories exist or not, how to append text from file and how to read line by line

Creating a filename

15 Curl in scripts

16 Professional menus

Select loops and how to work with it

Needs a check statement.

17 Wait for filesystem events with inotify

Inotify is a linux kernel subsystem that acts to extend file systems. Whatever changes are made inotify will monitor the files and directories

18 Introduction to grep

19 Introduction to awk

Awk - scripting language used to manipulate data and generate reports

20 Introduction to sed

Sed stands for stream editor and can be used to manipulate text files

21 - Debugging Bash Scripts

Bash offers an extensive debugging facility so you know if it doesn’t go according to plan. The error includes the line and where the error is

Bash -x shows you the code that is being executed.

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