Parsing a CSV file using gawk

Question

How do you parse a CSV file using gawk? Simply setting FS="," is not enough, as a quoted field with a comma inside will be treated as multiple fields.

Example using FS="," which does not work:

file contents:

one,two,"three, four",five
"six, seven",eight,"nine"

gawk script:

BEGIN { FS="," }
{
  for (i=1; i<=NF; i++) printf "field #%d: %s\n", i, $(i)
  printf "---------------------------\n"
}

bad output:

field #1: one
field #2: two
field #3: "three
field #4:  four"
field #5: five
---------------------------
field #1: "six
field #2:  seven"
field #3: eight
field #4: "nine"
---------------------------

desired output:

field #1: one
field #2: two
field #3: "three, four"
field #4: five
---------------------------
field #1: "six, seven"
field #2: eight
field #3: "nine"
---------------------------

Answer 1

If permissible, I would use the Python csv module, paying special attention to the dialect used and formatting parameters required, to parse the CSV file you have.

Answer 2

{
  ColumnCount = 0
  $0 = $0 ","                           # Assures all fields end with comma
  while($0)                             # Get fields by pattern, not by delimiter
  {
    match($0, / *"[^"]*" *,|[^,]*,/)    # Find a field with its delimiter suffix
    Field = substr($0, RSTART, RLENGTH) # Get the located field with its delimiter
    gsub(/^ *"?|"? *,$/, "", Field)     # Strip delimiter text: comma/space/quote
    Column[++ColumnCount] = Field       # Save field without delimiter in an array
    $0 = substr($0, RLENGTH + 1)        # Remove processed text from the raw data
  }
}

Patterns that follow this one can access the fields in Column[]. ColumnCount indicates the number of elements in Column[] that were found. If not all rows contain the same number of columns, Column[] contains extra data after Column[ColumnCount] when processing the shorter rows.

This implementation is slow, but it appears to emulate the FPAT/patsplit() feature found in gawk >= 4.0.0 mentioned in a previous answer.

Reference

Answer 3

Here's what I came up with. Any comments and/or better solutions would be appreciated.

BEGIN { FS="," }
{
  for (i=1; i<=NF; i++) {
    f[++n] = $i
    if (substr(f[n],1,1)=="\"") {
      while (substr(f[n], length(f[n]))!="\"" || substr(f[n], length(f[n])-1, 1)=="\\") {
        f[n] = sprintf("%s,%s", f[n], $(++i))
      }
    }
  }
  for (i=1; i<=n; i++) printf "field #%d: %s\n", i, f[i]
  print "----------------------------------\n"
}

The basic idea is that I loop through the fields, and any field which starts with a quote but does not end with a quote gets the next field appended to it.