Remove \n newline if string contains keyword - regex

Question

I'd like to know if I can remove a \n (newline) only if the current line has one ore more keywords from a list; for instance, I want to remove the \n if it contains the words hello or world.
Example:
this is an original
file with lines
containing words like hello
and world
this is the end of the file
And the result would be:
this is an original
file with lines
containing words like hello and world this is the end of the file
I'd like to use sed, or awk and, if needed, grep, wc or whatever commands work for this purpose. I want to be able to do this on a lot of files.

Answer 1

Using awk you can do:
awk '/hello|world/{printf "%s ", $0; next} 1' file
this is an original
file with lines
containing words like hello and world this is the end of the file

Answer 2

here is simple one using sed
sed -r ':a;$!{N;ba};s/((hello|world)[^\n]*)\n/\1 /g' file
Explanation
:a;$!{N;ba} read whole file into pattern, like this: this is an original\nfile with lines\ncontaining words like hell\
o\nand world\nthis is the end of the file$
s/((hello|world)[^\n]*)\n/\1 /g search the key words hello or world and remove the next \n,
g command in sed substitute stands to apply the replacement to all matches to the regexp, not just the first.

Answer 3

A non-regex approach:
awk '
BEGIN {
# define the word list
w["hello"]
w["world"]
}
{
printf "%s", $0
for (i=1; i<=NF; i++)
if ($i in w) {
printf " "
next
}
print ""
}
'
or a perl one-liner
perl -pe 'BEGIN {#w = qw(hello world)} s/\n/ / if grep {$_ ~~ #w} split'
To edit the file in-place, do:
awk '...' filename > tmpfile && mv tmpfile filename
perl -i -pe '...' filename

Answer 4

This might work for you (GNU sed):
sed -r ':a;/^.*(hello|world).*\'\''/M{$bb;N;ba};:b;s/\n/ /g' file
This checks if the last line, of a possible multi-line, contains the required string(s) and if so reads another line until end-of-file or such that the last line does not contain the/those string(s). Newlines are removed and the line printed.

Answer 5

$ awk '{ORS=(/hello|world/?FS:RS)}1' file
this is an original
file with lines
containing words like hello and world this is the end of the file

Answer 6

sed -n '
:beg
/hello/ b keep
/world/ b keep
H;s/.*//;x;s/\n/ /g;p;b
: keep
H;s/.*//
$ b beg
' YourFile
a bit harder due to check on current line that may include a previous hello or world already
principle:
on every pattern match, keep the string in hold buffer
other wise, load hold buffer and remove \n (use of swap and empty the current line due to limited buffer operation available) and print the content
Add a special case of pattern in last line (normaly hold so not printed otherwise)