countMatchingPatterns

#Files:
#1.txt, 2.txt, 3.txt
#These files have some data which includeds "United States"

#Example 1:
#to count the number of occurrences of "United States" in all those files put together.
#This can be achieved using the below command:
grep "United States" *.txt | wc -l

#Example 2:
#Print only the matching string "United States" and not the entire line with matching string:
#This can be achieved using the below command:
grep -o "United States" *.txt

#Notes
#whether we use "-o" option or not, the count may be the same, if there is only one matching pattern per line
#"-o" option comes in handy when there are multiple matching patterns in a single line
# as the below example demonstrates
#===============================================================================================================================

grep "USA" multipleMatchesInSingleLine.txt
#output
#X lives in USA and Y lives in UK. Z lives in USA too.
#Do A, B and C live in USA?
#I think D lives in USA

grep -o "USA" multipleMatchesInSingleLine.txt
#Output
#USA
#USA
#USA
#USA

grep -o "USA" multipleMatchesInSingleLine.txt | wc -l
#Output
#4
grep  "USA" multipleMatchesInSingleLine.txt | wc -l
#Output
#3
#================================================================================================================================