sed就地命令未从bash中的文件中删除

Question

I have a bash script which checks for a string pattern in file and delete entire line i same file but somehow its not deleting the line and no throwing any error .same command from command prompt deletes from file .

#array has patterns
for k in "${patternarr[@]}
do
   sed -i '/$k/d' file.txt
done

sed version is >4

when this loop completes i want all lines matching string pattern in array to be deleted from file.txt

when i run sed -i '/pataern/d file.txt from command prompt then it works fine but not inside bash Thanks in advance

Answer 1

Here:

sed -i '/$k/d' file.txt

The sed script is singly-quoted , which prevents shell variable expansion. It will (probably) work with

sed -i "/$k/d" file.txt

I say "probably" because what it will do depends on the contents of $k , which is just substituted into the sed code and interpreted as such. If $k contains slashes, it will break. If it comes from an untrustworthy source, you open yourself up to code injection (particularly with GNU sed, which can be made to execute shell commands).

Consider k=^/ s/^/rm -Rf \\//e; # k=^/ s/^/rm -Rf \\//e; # .

It is generally a bad idea to substitute shell variables into sed code (or any other code). A better way would be with GNU awk:

awk -i inplace -v pattern="$k" '!($0 ~ pattern)' file.txt

Or to just use grep -v and a temporary file.

Answer 2

first of all, you got an unclosed double quote around ${patternarr[@]} in your for statement.

Then your problem is that you use single quotes in the sed argument, making your shell not evaluate the $k within the quotes:

% declare -a patternarr=(foo bar fu foobar)
% for k in ${patternarr[@]}; do echo sed -i '/$k/d' file.txt; done
sed -i /$k/d file.txt
sed -i /$k/d file.txt
sed -i /$k/d file.txt
sed -i /$k/d file.txt

if you replace them with double quotes, here it goes:

% for k in ${patternarr[@]}; do echo sed -i "/$k/d" file.txt; done
sed -i /foo/d file.txt
sed -i /bar/d file.txt
sed -i /fu/d file.txt
sed -i /foobar/d file.txt

Answer 3

Any time you write a loop in shell just to manipulate text you have the wrong approach. This is probably closer to what you really should be doing (no surrounding loop required):

awk -v ks="${patternarr[@]}" 'BEGIN{gsub(/ /,")|(",ks); ks="("ks")} $0 !~ ks' file.txt

but there may be even better approaches still (eg only checking 1 field instead of the whole line, or using word boundaries, or string comparison or....) if you show us some sample input and expected output.

Answer 4

You need to use double quotes to interpolate shell variables inside the sed command, like:

for k in ${patternarr[@]}; do
    sed -i "/$k/d" file.txt
done