sed-awk.txt

sed - STREAMLINE EDITOR , LETS YOU EDIT FILES WITH COMMANDS WITH NO NEED FOR A TEXT EDITOR
awk - POWERFUL METHOD FOR PROCESSING AND ANALYZING TEXT FILES - IN PARTICULAR DATA FILES ARE ORGANISED BY LINES AND COLUMNS 

SOURCES:
https://youtu.be/ixOiOS35HYg
https://youtu.be/M_T7Kb099pw

SED:
cat cities|sed 's/n/KA/p'  - 'substitute/find n/replace with KA/print'
's/n/KA/g/p' - 'substitute/find n/replace with KA/globally/print'
'/nairobi/s/n/KA/p' - 'find lines consist of word nairobi/substitute/find n/replace with KA/print'
's/hi/bye;s/hello/jello' - ; used in multiple substitutes
cat urls.txt|sed 's/^/https:\/\//' - ^ this means at start
cat urls.txt | sed '/^$/d' - ^ it means initial , $ means at the end , so all the white space at the initial and at the end will be removed
sed -r 's/[0-9]//g' - -r(regular expressions) , // means blank
sed 'y/abcdefghijklmnopqrstuvwxyz/ABCDEFGHIJKLMNOPQRSTUVWXYZ/' - change all the lower case to upper case

AWK:

cat cities|awk '{print $1}' - print the first column
cat urls.txt | awk -F '.' '{print $1}' - print everything which is coming before .

CUT 

https://youtu.be/eHGCxEVlHd0

SORT
The sort command is used in Linux to print the output of a file in given order. This command processes on your data (the content of the file or output of any command) and reorders it in the specified way, which helps us to read the data efficiently.09-Sept-2020

DIFF
diff is a command-line utility that allows you to compare two files line by line. It can also compare the contents of directories. The diff command is most commonly used to create a patch containing the differences between one or more files that can be applied using the patch command.

test
check file types and compare values -gt , -lt etc

IF A COMMAND IS NOT AN EXECUTABLE OR A SHELL BUILTIN , IT WILL SEARCH FOR THE COMMAND ON PATH ENVIRONMENT VARIABLES