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I am manipulating data from a text file with the following data structure:

"1111","2222","3333","4444","5555","6666","7777","2017/12/15 16:26:00"

I am trying to change the '/' in the date to '-'. Here is my awk command:

awk -F "," '{gsub("/", "-", $8); print}' my-input.txt

It successfully changes the /, but has the unintended consequence of replacing the ',' commas with a ' ' space character:

"1111" "2222" "3333" "4444" "5555" "6666" "7777" "2017-12-15 16:26:00"

Does anyone know why this is happening?

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    awk -F "," 'BEGIN {OFS = ",";} {gsub("/", "-", $8); print}' my-input.txt or awk -F "," -v OFS="," '{gsub("/", "-", $8); print}' my-input.txt – taliezin Mar 1 '18 at 9:13
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    Right, if you define your input file separator to be ,, and you want to keep it, then you have to define your output file separator as well. – pfnuesel Mar 1 '18 at 9:16
  • Thank you, I overlooked defining the output file separator. – GustavMahler Mar 1 '18 at 9:23
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As pointed out by taliezin and pfnuesel, when defining the input file separator as a ',' it is necessary to also define the output file separator as a ',' to keep it. If the output file separator is omitted and a modification to an existing field has been done, awk will use the default value, in this case a ' ' [space] character.

The below is the corrected awk command:

awk -F "," -v OFS="," '{gsub("/", "-", $8); print}' my-input.txt

Which outputs the intended result which maintains the ',':

"1111","2222","3333","4444","5555","6666","7777","2017-12-15 16:26:00"
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    To be more specific: The output file separator needs to be defined if awk is provoked to re-form its fields. This happens when you modify a field. If no modification to existing fields is done, the separator will be kept. – Kusalananda♦ Mar 1 '18 at 9:56
  • Thanks for the input Kusalananda. I've updated my answer. – GustavMahler Mar 1 '18 at 10:44
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Since the requirement is to "change the '/' in the date to '-'", which is a simple character substitution, why not use sed? sed 's///-/g' my-input.txt

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    Because I know how to target a single field using awk ($8), whereas I don't know how to achieve that using sed. By targeting a single field (column), it eliminates unwanted global substitutions occurring. – GustavMahler Mar 1 '18 at 18:10

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