Converting lines in chunks into tab delimited

Question

I have the following lines in 2 chunks (actually there are ~10K of that). And in this example each chunk contain 3 lines. The chunks are separated by an empty line. So the chunks are like "paragraphs".

xox
91-233
chicago

koko
121-111
alabama

I want to turn it into tab-delimited lines, like so:

xox  91-233  chicago
koko 121-111 alabama

How can I do that?

I tried tr "\n" "\t", but it doesn't do what I want.

Answer 1

$ awk -F'\n' '{$1=$1} 1' RS='\n\n' OFS='\t' file
xox     91-233  chicago
koko    121-111 alabama 

How it works

Awk divides input into records and it divides each record into fields.

• -F'\n'

  This tells awk to use a newline as the field separator.

• $1=$1

  This tells awk to assign the first field to the first field. While this seemingly does nothing, it causes awk to treat the record as changed. As a consequence, the output is printed using our assigned value for ORS, the output record separator.

• 1

  This is awk's cryptic shorthand for print the line.

• RS='\n\n'

  This tells awk to treat two consecutive newlines as a record separator.

• OFS='\t'

  This tells awk to use a tab as the field separator on output.

Answer 2

<sup>This answer offers the following:
* It works with blocks of nonempty lines of any size, separated by any number of empty lines; John1024's helpful answer (which is similar and came first) works with blocks of lines separated by exactly one empty line.
* It explains the awk command used in detail.</sup>

A more idiomatic (POSIX-compliant) awk solution:

awk -v RS= -F '\n' -v OFS='\t' '$1=$1""' file

• -v RS= tells awk to operate in paragraph mode: consider each run of nonempty lines a single record; RS is the input record separator.

  • Note: The implication is that this solution considers one or more empty lines as separating paragraphs (line blocks); empty means: no line-internal characters at all, not even whitespace.

• -F '\n' tells awk to consider each line of an input paragraph its own field (breaks the multiline input record into fields by lines); -F sets FS, the input field separator.

• -v OFS='\t' tells awk to separate fields with \t (tab chars.) on output; OFS is the output field separator.

• $1=$1"" looks like a no-op, but, due to assigning to field variable $1 (the record's first field), tells awk to rebuild the input record, using OFS as the field separator, thereby effectively replacing the \n separators with \t.

  • The trailing "" is to guard against the edge case of the first line in a paragraph evaluating to 0 in a numeric context; appending "" forces treatment as a string, and any nonempty string - even if it contains "0" - is considered true in a Boolean context - see below.

• Given that $1 is by definition nonempty and given that assignments in awk pass their value through, the result of assignment $1=$1"" is also a nonempty string; since the assignment is used as a pattern (a condition), and a nonempty string is considered true, and there is no associated action block ({ ... }), the implied action is to print the - rebuilt - input record, which now consists of the input lines separated with tabs, terminated by the default output record separator (ORS), \n.