Bash - Deleting a line from file using sed

Question

Probably a pretty straight forward one but I'm fairly new to bash I'm trying to delete a line from a .txt file that contains a specific string. The string is specified as a variable "$logline"

My code for sed is currently:

logline="example2"
sed -i "/$logline/d" > /root/file.txt

The contents of the /root/file.txt file is...

/root/Dir/example.txt
/root/Dir2/example2.txt
/root/Dir/example3.html
...

I expect just the line /root/Dir2/example2.txt to be deleted.

However when I run this the entire txt file is getting wiped, and I get the error message sed: no input files .

Any idea what I'm missing here?

Thanks

Answer 1

sed -i has no output, so when you redirect to a file it will just be truncated.

Instead, give the filename to sed directly without redirecting:

sed -i "/$logline/d" /root/file.txt

Answer 2

If your variable $logline contains exact text to be matched , sed is probably the wrong program to be using. Pattern addresses are regular expressions, and you'll need to escape any of the metacharacters understood in basic REs, including \\ , * and . .

For removing a fixed string, you'll probably find it easier to use grep -Fv ; something like

grep -Fv -- "$logline" <"$file" >"$file.new"; mv "$file.new" "$file"

If you really must use sed, you should choose whether you're editing in-place with -i or using standard output - you don't get both. So either

•  sed -i "/$logline/d" "$file" 

•  sed "/$logline/d" "$file" >"$file.new" && mv "$file.new" "$file"