Using Sed with Regex

Question

I would need to edit the values in a file delimited by colons (:)

I would like to replace the contents of the file by using regular expression. After a grep to confirm that the item exist in the file system. I would like to edit the contents inside it by using sed.

I am open to the use of others tools. That would help me.

EDIT:

So far i have been trying to use sed to modify the contents in the text file in test.txt. The current solution i could think of is sed.

 sed -i "s/^\($newEvent:$newPerson:[^:]*\):[^:]*:/\1:$newQty:/" test.txt 
 echo "item Qty has been updated successfully!"

Is there a way i am able to edit the content after a string matching of event && person and modify the contents of that line which matches.

Before any input content in text file

Birthday Party:John Harris:1:10:1

Enter Event: Birthday Party
Enter Person: John Harris


a)  Update Event
b)  Update Person
c)  Price
d)  Update Item brought
e)  Update Quantity Sold 
f)  Back to main menu
Please enter your choice: d
New Qty Sold : 38
Qty Sold  has been updated successfully!

a)  Update Event
b)  Update Person
c)  Update Item brought
d)  Update Quantity Sold
e)  Back to main menu
Please enter your choice: f

After input content in text file

 Birthday Party:John Harris:1:10:1

Answer 1

It is unclear what exactly it is you want, but how about using read or awk?

echo -e "Happy Birthday:Mom Annie:12.99:197:101\nMeow Meow:Dad:11.11:1:1" | while IFS=: read -r event person date num1 num2 _ ; do echo $person; done

echo -e "Happy Birthday:Mom Annie:12.99:197:101\nMeow Meow:Dad:11.11:1:1" | awk -F: '$1 ~ /Happy.*/{print $1, $3, $NF}'
echo -e "Happy Birthday:Mom Annie:12.99:197:101\nMeow Meow:Dad:11.11:1:1" | awk -F: '$1 ~ /Happy.*/{print $0}'

Relevant: http://www.pement.org/awk/awk1line.txt

Consider rephrasing your question by showing the input and desired output.

Answer 2

For more complex text munging tasks consider using e.g. Perl or Python, or even awk (presumably in the base install of your system). sed(1) is fine as far as it goes, but it's syntax is arcane (and more suited for one-shot tasks, IMVHO).