How to print columns one after the other in bash?

Question

Is there any better methods to print two or more columns into one column, for example

input.file

AAA    111
BBB    222
CCC    333

o

Answer 1

You can use a GNU awk array of arrays to store all the data and print it later on.

If the number of columns is constant, this works for any amount of columns:

gawk '{for (i=1; i<=NF; i++)            # loop over columns
           data[i][NR]=$i               # store in data[column][line]
      }
      END {for (i=1;i<=NR;i++)          # loop over lines
                for (j=1;j<=NF;j++)     # loop over columns
                     print data[i][j]   # print the given field
      }' file

Note NR stands for number of records (that is, number of lines here) and NF stands for number of fields (that is, the number of fields in a given line).

If the number of columns changes over rows, then we should use yet another array, in this case to store the number of columns for each row. But in the question I don't see a request for this, so I am leaving it for now.

See a sample with three columns:

$ cat a
AAA    111  123
BBB    222  234
CCC    333  345
$ gawk '{for (i=1; i<=NF; i++) data[i][NR]=$i} END {for (i=1;i<=NR;i++) for (j=1;j<=NF;j++) print data[i][j]}' a
AAA
BBB
CCC
111
222
333
123
234
345

---

If the number of columns is not constant, using an array to store the number of columns for each row helps to keep track of it:

$ cat sc.wk 
{for (i=1; i<=NF; i++)
       data[i][NR]=$i
 columns[NR]=NF
}
END {for (i=1;i<=NR;i++)
            for (j=1;j<=NF;j++)
                 print (i<=columns[j] ? data[i][j] : "-")
}
$ cat a
AAA    111  123
BBB    222
CCC    333  345
$ awk -f sc.wk a
AAA
BBB
CCC
111
222
333
123
-
345