How to add characters in word and replace it using sed command in linux

I have one requirement.

I have one text file named as a.txt, which is having list of words –

GOOGLE
FACEBBOK

Now I have one another file named as b.txt , which is having content as

Company name is google.
Company name is facebook.

Like this n of lines are there with different different words.

Then I am writing script file –

    FILENAME="a.txt"

SCHEMA=$(cat $FILENAME)

for L in $SCHEMA
do
    echo "${L,,}"

sed -i -E "s/.+/L&_/" b.txt
done

So after running script the output file of b.txt file I am expecting is

 Company name is google_
 Company name is facebook_

But the output after running that script I am getting is –

Company name is google.__
Company name is facebook.__

And this output will be saved in b.txt file as I mentioned in sed command

Note – In a.txt I am having the list of Words which I want to replace and in b.txt file I am having paragraphs of line in which I am having words like google. , facebook. and so on.

So that’s why I am not able to give direct sed command for replacement.

I hope that you understand my requirement.

Thanks in advance!

Answer

You can use the following GNU sed solution:

FILENAME="a.txt"
while IFS= read -r L; do
  sed -i "s/($L)./1_/gI" b.txt
done < $FILENAME

Or, the same without a loop as a single line (as used in anubhava’s answer):

sed -i -f <(printf 's/\(%s\)\./\1_/gIn' $(<"$FILENAME")) b.txt

With the script, you

• while IFS= read -r L; do – read the file line by line, each line being assigned to L
• sed -i "s/($L)./1_/gI" b.txt – replaces all occurrences of L (captured into Group 1 with the help of capturing (...) parentheses) followed with . (in a case insensitive way due to I flag) in b.txt with the same value as captured in Group 1 and _ appended to it.
• -f allows passing a list of commands to sed
• printf 's/\(%s\)\./\1_/gIn' $(<"$FILENAME") creates a list of sed commands, in this case, it looks like

s/(GOOGLE)./1_/gI
s/(FACEBOOK)./1_/gI