Concatenating fields from lines with different numbers of fields

awksedtext processing

Given input like this:

x y a b c t
p q w w t
a b c d
p q r

I'd like to concatenate fields from field 3 up to but not including the last one. If field 3 is the last field, I'd like to insert a placeholder. So given the input above, this is the preferred output:

x y a_b_c t
p q w_w t
a b c d
p q _ r

The end result is that all lines will have four fields. Is this possible in awk or cut or sed, etc?

Best Answer

awk '{
  s = m = ""
  for (i = 3; i < NF; i++) {m = m s $i; s = "_"}
  if (m == "") m = "_"
  print $1, $2, m, $NF}'

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How to you combine all lines that end with a backslash character

a shorter and simpler sed solution:

sed  '
: again
/\\$/ {
    N
    s/\\\n//
    t again
}
' textfile

or one-liner if using GNU sed:

sed ':x; /\\$/ { N; s/\\\n//; tx }' textfile

Sed – Replacing Lines Containing a Pattern

sed '/^[[:alpha:]]/{$!N;s/\n/       /;}' <<\DATA
NAME_A
12,1
NAME_B
21,2
DATA

OUTPUT

NAME_A  12,1
NAME_B  21,2

That addresses lines beginning with a letter, pulls in the next if there is one, and substitutes a tab character for the newline.

note that the s/\n/<tab>/ bit contains a literal tab character here, though some seds might also support the \t escape in its place

To handle a recursive situation you need to make it a little more robust, like this:

sed '$!N;/^[[:alpha:]].*\n[^[:alpha:]]/s/\n/    /;P;D' <<\DATA
NAME_A
NAME_B
12,1  
NAME_C
21,2
DATA

OUTPUT

NAME_A
NAME_B  12,1
NAME_C  21,2

That slides through a data set always one line ahead. If two ^[[:alpha:]] lines occur one after the other, it does not mistakenly replace the newline, as you can see.

Best Answer

Related Solutions

How to you combine all lines that end with a backslash character

Sed – Replacing Lines Containing a Pattern

OUTPUT

OUTPUT

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