What defines a "column" in bash? In awk? - bash

Question

I was viewing this question: Bash - Take nth column in a text file
I want to make a function that writes to a textfile that I can then parse using the method above. So, for example, I want my function to write 'dates' in the first column, 'ID's in the second column, and 'addresses' in the third column. Then once I have this, a user could, for example, see if a certain ID is present in the file by querying for the second column, then looking at each item there. The user could do this using the method discussed in the question above.
What defines a column? Is it just a space delimiter? Is it a tab?
If I want to output this information as stated above, what would the method where I write to the file look like? So far I have:
cat "$DATE $ID $ADDRESS \n" > myfile.data

Answer 1

In bash, as opposed to awk, columns are separated by characters in IFS.
That is to say, if you set:
IFS=$'\t'
...then columns, as understood by bash builtins such as read first second rest, will be separated by tabs. On the output side, printf '%s\n' "${array[*]}" will print the items in the array array separated by the first character of IFS.
The default value of IFS is equivalent to $' \t\n' -- that is, the space, the tab, and the newline character.
To write a file with a delimiter of your choice, and (presumably) more than one row (replace the while read with however you're actually getting your data, or only use the inside of the loop if you're only writing one line):
while read -r date id address; do
printf '%s\t' "$date" "$id" "$address" >&3; printf '\n' >&3
done 3>filename
...or, if you don't want the trailing tab left by the above:
IFS=$'\t' # use a tab as the field separator for output
while IFS=$' \t\n' read -r date id address; do
entry=( "$date" "$id" "$address" )
printf '%s\n' "${entry[*]}" >&3
done 3>filename
Putting 3>filename on the outside of the loop is much more efficient than >>filename on each line, which re-opens the output file once per line written.

Answer 2

If you're going to use awk, the columns are separated by the field separator. See FS in man awk for details.
Most tools support some ways of changing the column separator:
cut -f
sort -t
bash itself uses the IFS variable (Internal Field Separator) for word splitting.
cat awaits file as an argument. To output a string, use echo instead.

Answer 3

If we are talking about awk then the space character is the default column separator.
Its easy to change what is used as the "Field Separator" (FS) when awk is parsing a file: awk '{FS=",";print $2}'. Will use comma as the separator (note: does not respect quotes and stuff like a csv parser).
To write to the file I would use echo and the double carrot >>.
>> appends whereas > rewrites the file.
echo -e will let echo recognize \n and similar special chars
So the command would be
echo -e "$DATE $ID $ADDRESS \n" >> myfile.data