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Accepted
Nicola Gambaro
Asked: 2019-10-20 14:15:14 +0800 CST

How to make a Bash script to change the format of a date in a CSV file

  • 772

I've got a series of CSV files whose second field is dates:

R.OUSE BOURTON MILL,2000-03-22T14:50:00,Ammoniacal Nitrogen as N,0.03,mg/l

How can I change the date format into DD/MM/YYYY for all files? The measurement time is not needed.

Thank you so much

scripts bash text-processing csv

4 Answers

  1. Best Answer

    With miller, using its builtin strptime and strftime functions :

    $ mlr --fs ',' --ocsvlite --headerless-csv-output put '
    $2 = strftime(strptime($2,"%Y-%m-%dT%H:%M:%S"),"%d/%m/%Y")
  ' file.csv
R.OUSE BOURTON MILL,22/03/2000,Ammoniacal Nitrogen as N,0.03,mg/l
    • 7

  2. Why bash?

    From command line:

    sed -E 's,([0-9]{4})-([0-9]{2})-([0-9]{2}),\3/\2/\1,g' test

    Result:

    R.OUSE BOURTON MILL,22/03/2000T14:50:00,Ammoniacal Nitrogen as N,0.03,mg/l
    • 2

  3. Here's a reasonable solution using bash and date:

    #!/bin/bash

IFS=,
while read -r line; do
    fields=($line) # Split string into fields
    fields[1]=$(date --date="${fields[1]}" +%d/%m/%Y) # Transform the second date
    echo "${fields[*]}" # Reassemble fields
done <file.csv >>output.csv
    • 1

  4. Match and rearrange time components with awk gensub.

    $ awk 'BEGIN {FS=OFS=","} {$2=gensub(/(.+)-(.+)-(.+)T.*/,"\\3/\\2/\\1","g",$2)} 1' file.csv # >> output.csv

    (nawk version):

    $ awk 'BEGIN {FS=OFS=","} {split(substr($2,0,10),a,"-"); $2=sprintf("%s/%s/%s",a[3],a[2],a[1])} 1' file.csv # >> output.csv

    if the intention is to only convert the time format, then epoch is probably a better choice.

    #!/usr/bin/awk -f
#
# example.awk
#
BEGIN {
    FS=OFS=","
} {
    split(substr($2,0,10),a,"-")
    $2=mktime(sprintf("%s %s %s %s %s %s",a[1],a[2],a[3],00,00,00))
} 1

    $ awk -f example.awk file.csv # >> output.csv
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