Replacing a character plus newline with a string-CodePudding

Taking a file with DHCP host definitions as input I need to transform entries like:

host mx {
 fixed-address 10.0.1.161;

into entries like this:

host mx - fixed-address 10.0.1.161;

(obviously I need to output this to stdout, not replace those entries in place)

sed doesn't work because it basically doesn't allow replacing newlines.

CodePudding user response：

sed is able to delete the newline:

$ printf 'host mx {\n  fixed-address 10.0.1.161;\n' | sed '/{$/{N; s/{\n */- /; }' 
host mx - fixed-address 10.0.1.161;

This command deletes the final { and the newline on all lines that end in {, which may not be quite what you want. If the mx records you are trying to change are multi-line, you'll need to add more logic, and perhaps you want to limit this further with /host mx {^/ ..., but you would need to add more detail to the question.

CodePudding user response：

With a very short Perl one liner:

$ perl -pe 's/{\n/-/ms' file
host mx - fixed-address 10.0.1.161;

CodePudding user response：

Here is an awk to do what is described:

printf 'host mx {\n  fixed-address 10.0.1.161;\n' | awk -F "[ \t]*\\\{" '/^host mx/{
    getline l2
    sub(/^[ \t]*/,"",l2)
    printf "%s - %s\n", $1, l2
}'

Prints:

host mx - fixed-address 10.0.1.161;