sed erasing everything instead of changing single field - shell

Question

hi i have this code that is meant to update a single field title but it ended with it erasing everything. need some help please
BookDB.txt:
The Hunger Games:Suzanne Collins:1:1:1
Weapon X:Stan Lee:1:1:1
Weapon X:stan lim:1:1:1
function update_title
{
echo "Title: "
read title
echo "Author: "
read author
grep -iqs "$title:$author:" BookDB.txt && echo "Book Found!"
echo "New Title: "
read title_new
sed -i "/^$author:/ s/$title/$title_new/" BookDB.txt || tee BookDB.txt && echo "Book Title has been updated sucessfully!"
}

Answer 1

Answer for Revised Question
The sed command needs to be changed because the title comes first on the line, not the author. Also the tee command removed for the same reasons as explained below. Thus, define the function as follows:
update_title ()
{
echo "Title: ";
read title;
echo "Author: ";
read author;
grep -iqs "$title:$author:" BookDB.txt && echo "Book Found!";
echo "New Title: ";
read title_new;
sed -i "/:$author:/ s/^$title/$title_new/" BookDB.txt && echo "Book Title has been updated sucessfully!"
}
As an example, invoke the function:
$ update_title
Title:
Weapon X
Author:
Stan Lee
Book Found!
New Title:
Weapon XYZ
Book Title has been updated sucessfully!
The result is:
$ cat BookDB.txt
The Hunger Games:Suzanne Collins:1:1:1
Weapon XYZ:Stan Lee:1:1:1
Weapon X:stan lim:1:1:1
Answer for Original Question
Replace:
sed -i "/^$author:/ s/$title/$title_new/" BookDB.txt || tee BookDB.txt && echo "Book Title has been updated sucessfully!"
With this:
sed -i "/^$author:/ s/$title/$title_new/" BookDB.txt && echo "Book Title has been updated sucessfully!"
The first line asks sed to rewrite BookDB.txt in place. It then asks tee to overwrite the same file. The solution is to do the first only.
Explanation
Commands such as:
sed 's/old/new/' file >file
or:
sed 's/old/new/' file | tee file
will be unreliable. They attempt to read from a file while writing to it at the same time. Depending on how files are buffered, this type of command may occasionally work but are never to be trusted.
sed -i is specifically designed to avoid this issue. It writes to a temporary file and, after all changes have been successfully save, then overwrites the source file.
Example
Let's define this function:
function update_title
{
echo "Title: "
read title
echo "Author: "
read author
grep -iqs "$title:$author:" BookDB.txt && echo "Book Found!"
echo "New Title: "
read title_new
sed -i "/^$author:/ s/$title/$title_new/" BookDB.txt && echo "Book Title has been updated sucessfully!"
}
Now, let's use it:
$ cat BookDB.txt
Tim:Old Title:
Tom:Older Title:
$ update_title
Title:
Old Title
Author:
Tim
New Title:
New Title
Book Title has been updated sucessfully!
$ cat BookDB.txt
Tim:New Title:
Tom:Older Title:
The old title was successfully replaced.
Warning
This function substitutes shell variables directly into sed commands. If the user is unaware of the power of sed-active characters, the results may be surprising.
As an example:
$ update_title
Title:
.*
Author:
Tim
New Title:
This & That
Book Title has been updated sucessfully!
Now, observe the new file:
$ cat BookDB.txt
This Tim:New Title: That
Tom:Older Title:
OSX
On OSX, the -i option to sed requires an argument. For OSX, and possibly other BSD platforms, replace the sed line in the function definition with:
sed -i .bak "/^$author:/ s/$title/$title_new/" BookDB.txt && echo "Book Title has been updated sucessfully!"
Or,
sed -i "" "/^$author:/ s/$title/$title_new/" BookDB.txt && echo "Book Title has been updated sucessfully!"

Answer 2

use this , because first field is definitely the title so you have to put title infront
sed -i "/^$title:$author:/ s/$title/$title_new/" BookDB.txt