I have four files named source, correct, wrong and not_found. I am trying to write a script in bash wherein I read each line from file named source, store the line as variable x, and match it against a condition.
If it passes, then I need to write that line to file named correct, but the catch is before writing into correct I need to check if the variable x is currently present in file named wrong and if yes delete it and then add the line to file named correct.
I have tried below, but it doesn't modify the file and neither gives me any output:
sed -i '/$x/d' ./wrong
As you have already understood, variables inside '...' are not expanded.
If you replace the single-quotes with double-quotes,
this will delete the matching line from ./wrong:
sed -i "/$x/d" ./wrong
But you also want to add the line to ./correct, if there was a match.
To do that, you can run grep before the sed:
grep "$x" ./wrong >> ./correct
This will have the desired effect,
but sed will overwrite ./wrong, even when it doesn't need to.
You can prevent that like this:
if grep "$x" ./wrong >> ./correct; then
sed -i "/$x/d" ./wrong
fi