How can I "merge" patterns in a single line?

Question

I am doing grep and sed and I get 2 lines of a file that I am interested in. How can I get these lines in a single line ending with the new line character?
Now I am getting:

pattern1  
pattern2  

I would like to get pattern1 pattern2 \n

Solution 1

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

Solution 2

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.

Solution 3

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.

Solution 4

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

Solution 5

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.

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Comments

[slm]

Can you share more of the sample data?

[slm]

Paste is the tool for the job, if you're intending to merge multiple lines of output into one.

[Ludwig Schulze]

any specific tool? How do you plan to do this?

[Jim]

What is - -? Is the command like that?

[Angel Todorov]

unquoted, the variable is also subject to filename expansion, so if you have any glob characters (like * or ?) in the result, the values may change.

[Nidal]

@glennjackman, thanks for mention this, how can we fix this?

[Marek Zakrzewski]

@Networker by not using backticks but $() instead.. and using printf printf '%s\n' "$x"

[Angel Todorov]

I would expect that printf '%s\n' "$x" will NOT remove the "internal" newline.

[Angel Todorov]

The tr solution will swallow the ending newline, so you might want to add ; echo to that one

[Marek Zakrzewski]

@glennjackman ah right! Thanks for the hint. You are free to modify the answer though. I missed that bit!

[slm]

@Jim - yes that's correct. Those are telling paste how you want it to process the input. 2 at a time. Add more to do 3 at at time. seq 10 | paste -d " " - - .

[Angel Todorov]

Uh, no. That will execute the output of the sed command.