How can I “merge” patterns in a single line?

paste:

{...pipeline...} | paste -d " " - -

That says: "read a line from stdin (the first -), read another line from stdin (the second -), then join them with a space"

a bash-specific technique:

$ x=$(grep -o pattern. test.txt)
$ echo "$x"
pattern1
pattern2
$ mapfile -t <<< "$x"
$ echo "${MAPFILE[*]}"
pattern1 pattern2

ref: http://www.gnu.org/software/bash/manual/bashref.html#index-mapfile

I'll put three versions different methods in a row

AWK

printf %s\\n pattern1 pattern2 | awk -vRS="\n" -vORS=" " '1; END {print RS}'

SED

printf %s\\n pattern1 pattern2 | sed '$!N;s/\n/ /'

TR

printf %s\\n pattern1 pattern2 | tr '\n' ' '; echo

And there are many more.

you can do it using shell script or in command-line, just put the output of the command in a variable then echo it:

# x=$(grep -e "pattern1\|pattern2" test)
# printf '%s\n' "$x"
pattern1 pattern2

With sed, you can do this:

<your previous commands> | sed '{N; s/\n/ /}'

• N; tells sed to add the next line into the pattern space, so now sed is working with both lines.
• s/\n/ / replaces the newline character with a space, "merging" the two lines together.

A simple way, pipe output to xargs:

$ echo -e 'a\nb' | xargs
a b

This only works with small ouput, because it's limited by maximum characters per command line. The largest value depends on system, you can get this value using getconf ARG_MAX.

( set -f; IFS='
'; printf '%s %s\n' $(grepcmd <input)
) >output

IFS will be happy to eat it if you want.

wrap your sed/grep in backticks

when your original command was:

grep -i 'foo' mylog.log | sed 's/bar/baz/gi'

your new command would be:

`grep -i 'foo' mylog.log | sed 's/bar/baz/gi'`

Doesn't get the spaces in between lines, but you can always tack on another sed pipe:

 | sed 's/$/ /'