How to sort an array of strings using substring with Bash

Question

I am writing my first unix bash script and I find it really difficult because I've never used linux before. It is homework from university. I tried a lot of stuff and I've been looking for hours but I simply can't find the right solution. Can someone give me some directions of what to use to sort strings from array which look like this:

room_100056.dat 4
room_8973.dat 2
room_7764.dat 1
room_2092.dat 20

to this:

room_7764.dat 1
room_8973.dat 2
room_10056.dat 4
room_2092.dat 20

When sorting the initial array, I am creating a new array which contains the sorted data. The problem is that in the sorted array, the data is printed like this:

room_100056.dat 
room_8973.dat
room_7764.dat 
room_2092.dat
1
2
4
20

Code:

file=$1/*.dat

count_visits=()

for room in $file
do
   visits=$(grep "<Visit>" $room | wc -l)
   filename=$(basename $room)
   count_visits+=($filename$'\t'$visits)
done

sorted_visits=($(echo ${count_visits[@]} | tr " " "\n" | sort -g))
printf '%s\n' "${sorted_visits[@]}"
exit

You'll have bugs if your filenames have spaces unsell modifying count_visits+=( "$filename"$'\t'"$visits" ), and similarly quoting "$room". In general, you should probably run this code through shellcheck.net and follow its advice. — Charles Duffy
– Charles Duffy, Commented Feb 25, 2018 at 3:33
(though actually, if you wanted everything to work right when filenames contain spaces, you'd put the number in the first column and the filename after it; that would also make it only sort -n needed, without the -k2). — Charles Duffy
– Charles Duffy, Commented Feb 25, 2018 at 17:27

choroba · Accepted Answer · 2018-02-25 08:52:47Z

2

Tell sort to use the second column numerically:

printf '%s\n' "${count_visits[@]}" | sort -k2n

edited Feb 25, 2018 at 8:52

answered Feb 25, 2018 at 1:43

choroba

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3 Comments

Charles Duffy Over a year ago

No reason not to make that printf '%s\n' "${count_visits[@]}" | sort -k2n and let the looping happen internally to printf.

choroba Over a year ago

@CharlesDuffy: I often forget about this functionality of printf. Thanks.

Simeon Enchev Over a year ago

Thank you for the suggestion. This worked great! I will further investigate sort because I guess I've missed something.

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