[BASH] Sorting by date and creating generic functions

[DietFlosser]

Hello again.

I'm currently using the following technique to sort a file called details.csv

sort -d -o details.csv -t , -k 3,3 details.csv

Within the csv file I only have 3 fields. A name, number and date of birth.

Example:

fred,999,03/04/2005
jane,888,01/01/1993
james,3456,12/01/1987
john,1234,11/08/1955

When I call the above sort, it is sorting the third field but it's doing so by the day (the format is dd/mm/yyyy). I'd love it to sort correctly by the entire date, or if it's too much hassle I'm happy to just sort by year.

I've tried playing around with the sort function, but this is the best way I can come up with without breaking everything. Hopefully one of you knowledgeable chaps can point me in the right direction.

Secondly, I have 2 functions that do the same job, but with different variables. Is there a way to just use one of these functions and return the "chopped" variable?

chop_name() {

	
	length=`echo ${#name}`
	
	if [ $length -gt 6 ]
	then
		name=`echo ${name:0:6}`
		name=$name".."
		cut="true"
	fi	
	
}

chop_number() {
	
	length=`echo ${#number}`
	
	if [ $length -gt 6 ]
	then
		number=`echo ${number:0:6}`
		number=$number".." #place dots at the end to show number's been chopped
		cut="true"
	fi	
}

Thanks again

[DietFlosser]

Bah.

I realised I was making it difficult for myself by having the date of birth LAST in the csv. I made it the first and used this sort:

sort -n -o details.csv -t"/" -k3 -k1 -k2 details.csv

Still, question 2 is still up for grabs :P

[Cabhan]

Did you think that Linux would let you down? Of course you can!

In this case, we are going to use a feature called indirect references. This allows you to use a variable to store another variable's name.

Let's see an example:

#!/bin/bash

foo=bar
bar=hello

echo "\$foo = $foo"
echo "\$\$foo = " $(eval echo \$$foo)

This produces the output:

$foo = bar
$$foo =  hello

We can use this ability to answer your question:

#!/bin/bash

chop_variable() {
    var_name=$1
    length=$(eval echo \${#$var_name})

    if [ "$length" -gt 6 ]; then
        new_value=$(eval echo \${$var_name:0:6})
        new_value=${new_value}..
    fi

    echo $new_value
}

chop_name() {
    name=$(chop_variable name)
}

chop_number() {
    number=$(chop_variable number)
}

name=hellotherefriend
number=1234567890

chop_name
chop_number

echo "name = $name"
echo "number = $number"

Give this a shot! Can you figure out how it works?

[DietFlosser]

Thanks very much Cabhan, that is ideal. I appreciate the explanation as well, it helps greatly!

I've only been playing with Bash on and off for a couple of weeks, but I have found it to be amazingly intuitive. There are a couple of odd niggles, like the fact functions only return a "state" rather than a value. Other than that, I've really enjoyed my time using bash.

[Giggidy]

CCCU by any chance?