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At the Linux/Unix command line, I want to turn this:


into this:


Is there a simple built-in command to do this, or does this require diving into Awk, Perl, etc.?

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3 Answers 3

up vote 6 down vote accepted

Don't know such built-in. Using Bash you can:

while read a && read b && read c ; do echo $a,$b,$c ; done < file
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If you have only 5 lines, you may not want to lose lines 4 and 5 just because you don't have line 6. –  musiphil Oct 16 '14 at 17:19

That is horrible, surely something like

tr \\n ' '

would do the same thing?

So for e.g. to join lines of the file *file_lines* use

cat file_lines | tr \\n ' '
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He didn't want all of it on a single line, it seems. –  l0b0 Feb 17 '12 at 10:42
Exactly. Referencing the problem statement, this would produce a single line with everything on it (A B C A B C A B C A B C A B C ...) which is not what was requested. –  Alan Krueger Feb 17 '12 at 17:08

Here is a solution in python:


def njoin(filename, outfn="", n=3, linesuffix=" "):
    if not outfn:
        outfn = filename + ".join"
    with open(filename) as infh, open(outfn, "w") as outfh:
        nline = 0
        for line in infh:
            if nline % n != n-1:
                line = line.rstrip() + linesuffix
            nline += 1

In your case you can use the function like this:

njoin("/path/to/file", n=3, linesuffixe=",")
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