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

Question

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 1

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_/gI\n' $(<"$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_/gI\n' $(<"$FILENAME") creates a list of sed commands, in this case, it looks like
s/\(GOOGLE\)\./\1_/gI
s/\(FACEBOOK\)\./\1_/gI

Answer 2

Here is how you can do it in a single shell command without any loop using gnu-sed with printf in a process substitution:
sed -i -E -f <(printf 's/\\b(%s)\\./\\1_/I\n' $(<a.txt)) b.txt
cat b.txt
Company name is google_
Company name is facebook_
This would be far more efficient than running sed or awk in a loop esp if input files are big in size.
printf command is creating a sed command script that looks like this:
s/\b(GOOGLE)\./\1_/I
s/\b(FACEBOOK)\./\1_/I
sed -f runs that dynamically generated script

Answer 3

With a single awk reading 2 Input_files could you please try following.
awk '
FNR==NR{
a[tolower($0)]
next
}
($(NF-1) in a){
sub(/\.$/,"")
print $0"_"
}
' a.txt FS="[ .]" b.txt
Explanation: Adding detailed explanation for above solution.
awk ' ##Starting awk program from here.
FNR==NR{ ##Checking condition FNR==NR which will be TRUE when a.txt is being read.
a[tolower($0)] ##Creating array a with index of current line in lower case from a.txt here.
next ##next will skip all further statements from here.
}
($(NF-1) in a){ ##Checking condition if 2nd last field is present in array a then do following.
sub(/\.$/,"") ##Substituting last DOT with NULL here.
print $0"_" ##Printing current line with _ here.
}
' a.txt FS="[ .]" b.txt ##Mentioning a.txt and setting field separator as space and . for b.txt here.
2nd solution: Adding 1 more solution with awk here.
awk '
FNR==NR{
a[tolower($0)]
next
}
{
sub(/\.$/,"")
}
($NF in a){
print $0"_"
}
' a.txt b.txt

Answer 4

This might work for you (GNU sed):
sed 's#.*#s/(&)./\\1_/Ig#' a.txt | sed -i -Ef - b.txt
N.B. The match is case insensitive because of the I flag on the substitution command, however the replacement is from the original file i.e. if the original string is google the match is case insensitive to GOOGLE and replaced by google_.