How to parse a CSV file in Bash?

How to parse a CSV file in Bash?

Coming late to this question and as bash do offer new features, because this question stand about bash and because none of already posted answer show this powerful and compliant way of doing precisely this.

Parsing CSV files under `bash`, using loadable module

Conforming to RFC 4180, a string like this sample CSV row:

12,22.45,"Hello, ""man"".","A, b.",42

should be splitted as

 1  12
 2  22.45
 3  Hello, "man".
 4  A, b.
 5  42

bash loadable .C compiled modules.

Under bash, you could create, edit, and use loadable c compiled modules. Once loaded, they work like any other builtin!! ( You may find more information at source tree. ;)

Current source tree (Oct 15 2021, bash V5.1-rc3) do contain a bunch of samples:

accept        listen for and accept a remote network connection on a given port
asort         Sort arrays in-place
basename      Return non-directory portion of pathname.
cat           cat(1) replacement with no options - the way cat was intended.
csv           process one line of csv data and populate an indexed array.
dirname       Return directory portion of pathname.
fdflags       Change the flag associated with one of bash's open file descriptors.
finfo         Print file info.
head          Copy first part of files.
hello         Obligatory "Hello World" / sample loadable.
...
tee           Duplicate standard input.
template      Example template for loadable builtin.
truefalse     True and false builtins.
tty           Return terminal name.
uname         Print system information.
unlink        Remove a directory entry.
whoami        Print out username of current user.

There is an full working cvs parser ready to use in examples/loadables directory: csv.c!!

Under Debian GNU/Linux based system, you may have to install bash-builtins package by

apt install bash-builtins

Using loadable bash-builtins:

Then:

enable -f /usr/lib/bash/csv csv

From there, you could use csv as a bash builtin.

With my sample: 12,22.45,"Hello, ""man"".","A, b.",42

csv -a myArray '12,22.45,"Hello, ""man"".","A, b.",42'
printf "%s\n" "${myArray[@]}" | cat -n
     1      12
     2      22.45
     3      Hello, "man".
     4      A, b.
     5      42

Then in a loop, processing a file.

while IFS= read -r line;do
    csv -a aVar "$line"
    printf "First two columns are: [ '%s' - '%s' ]\n" "${aVar[0]}" "${aVar[1]}"
done <myfile.csv

This way is clearly the quickest and strongest than using any other combination of bash builtins or fork to any binary.

Unfortunely, depending on your system implementation, if your version of bash was compiled without loadable, this may not work...

Complete sample with multiline CSV fields.

Here is a small sample file with 1 headline, 4 columns and 3 rows. Because two fields do contain newline, the file are 6 lines length.

Id,Name,Desc,Value
1234,Cpt1023,"Energy counter",34213
2343,Sns2123,"Temperatur sensor
to trigg for alarm",48.4
42,Eye1412,"Solar sensor ""Day /
Night""",12199.21

And a small script able to parse this file correctly:

#!/bin/bash

enable -f /usr/lib/bash/csv csv

file="sample.csv"
exec {FD}<"$file"

read -ru $FD line
csv -a headline "$line"
printf -v fieldfmt '%-8s: "%%q"\\n' "${headline[@]}"

while read -ru $FD line;do
    while csv -a row "$line" ; ((${#row[@]}<${#headline[@]})) ;do
        read -ru $FD sline || break
        line+=$'\n'"$sline"
    done
    printf "$fieldfmt\\n" "${row[@]}"
done

This may render: (I've used printf "%q" to represent non-printables characters like newlines as $'\n')

Id      : "1234"
Name    : "Cpt1023"
Desc    : "Energy\ counter"
Value   : "34213"

Id      : "2343"
Name    : "Sns2123"
Desc    : "$'Temperatur sensor\nto trigg for alarm'"
Value   : "48.4"

Id      : "42"
Name    : "Eye1412"
Desc    : "$'Solar sensor "Day /\nNight"'"
Value   : "12199.21"

You could find a full working sample there: csvsample.sh.txt or csvsample.sh.

Warning:

Of course, parsing CSV using this is not perfect! This work for many simple CSV files, but care about encoding and security!! For sample, this module won't be able to handle binary fields!

Read carefully csv.c source code comments and RFC 4180!

We can parse csv files with quoted strings and delimited by say | with following code

while read -r line
do
    field1=$(echo "$line" | awk -F'|' '{printf "%s", $1}' | tr -d '"')
    field2=$(echo "$line" | awk -F'|' '{printf "%s", $2}' | tr -d '"')

    echo "$field1 $field2"
done < "$csvFile"

awk parses the string fields to variables and tr removes the quote.

Slightly slower as awk is executed for each field.

From the man page:

-d delim The first character of delim is used to terminate the input line, rather than newline.

You are using -d, which will terminate the input line on the comma. It will not read the rest of the line. That's why $y is empty.

You need to use IFS instead of -d:

while IFS=, read -r col1 col2
do
    echo "I got:$col1|$col2"
done < myfile.csv

Note that for general purpose CSV parsing you should use a specialized tool which can handle quoted fields with internal commas, among other issues that Bash can't handle by itself. Examples of such tools are cvstool and csvkit.

How to parse a CSV file in Bash?