Printing column value in the next line

Question

My input is in TSV format:

C1
   r1
   r2
   r3
C2
   r1
   r3

Desired output is:

C1 r1
   r2
   r3
C2 r1
   r3

So, basically what I want is printing value of column 1 in next line, is it possible using Linux command?

Answer 1

With GNU sed:

$ sed -i.bak '/^[^[:blank:]]/{N;s/\n[[:blank:]]\+//;}' file
C1r1
  r2
  r3
C2r1
  r3

Answer 2

Possible solution is with awk:

awk '$1 ~ /C/ { p = 1; save = $1; } $1 !~ /C/ { if (p) { x = save $1; print x; p = 0; } else { print $0; } }' input

Result:

C1r1
  r2
  r3
C2r1
  r3

Answer 3

With ed:

$ ed -s input <<EOT
g/^C/+ s/^[[:space:]]*//
g/^C/  j                
w output
EOT