Issue
I am trying to delete the last three lines of a file in a shell bash script.
Since I am using local variables in combination with the Regex syntax in sed the answer proposed in How to use sed to remove the last n lines of a file does not cover this case. On the contrary, the cases covered deal with sed in a terminal and does not cover syntax in shell scripts, neither does it cover the use of variables in sed expressions.
The commands I have available is limited, since I am not on a Linux but use a MINGW64 for it. sed does a create job so far, but deleting the last three lines gives me some headaches in relation of how to format the expression.
I use wc to be aware of how many lines the file has and subtract then with expr three lines.
n=$(wc -l < "$distribution_area")
rel=$(expr $n - 3)
The start point for deleting lines is defined by rel but accessing the local variable happens through the $ and unfortunately the syntax of sed is using the $ to define the end of file. Hence,
sed -i "$rel,$d" "$distribution_area"
won't work, and what ever variant of combinations e.g. '"'"$rel"'",$d' gives me sed: -e expression #1, char 1: unknown command: `"' or something similar.
Can somebody show me how to combine the variable with the $d regex syntax of sed?
Solution
Can somebody show me how to combine the variable with the $d regex syntax of sed?
$d expands to a varibale d, you have to escape it.
"$rel,\$d"
or:
"$rel"',$d'
But I would use:
head -n -3 "$distribution_area" > "$distribution_area".tmp
mv "$distribution_area".tmp "$distribution_area"
Answered By - KamilCuk Answer Checked By - Dawn Plyler (WPSolving Volunteer)