Loop over tuples in bash?

Question

Is it possible to loop over tuples in bash?

As an example, it would be great if the following worked:

for (i,j) in ((c,3), (e,5)); do echo \"$i and $         


        

Answer 1

$ echo 'c,3;e,5;' | while IFS=',' read -d';' i j; do echo "$i and $j"; done
c and 3
e and 5

Answer 2

Using printf in a process substitution:

while read -r k v; do
    echo "Key $k has value: $v"
done < <(printf '%s\n' 'key1 val1' 'key2 val2' 'key3 val3')

Key key1 has value: val1
Key key2 has value: val2
Key key3 has value: val3

Above requires bash. If bash is not being used then use simple pipeline:

printf '%s\n' 'key1 val1' 'key2 val2' 'key3 val3' |
while read -r k v; do echo "Key $k has value: $v"; done

Answer 3

$ for i in c,3 e,5; do IFS=","; set -- $i; echo $1 and $2; done
c and 3
e and 5

About this use of set (from man builtins):

Any arguments remaining after option processing are treated as values for the positional parameters and are assigned, in order, to $1, $2, ... $n

The IFS="," sets the field separator so every $i gets segmented into $1 and $2 correctly.

Via this blog.

Edit: more correct version, as suggested by @SLACEDIAMOND:

$ OLDIFS=$IFS; IFS=','; for i in c,3 e,5; do set -- $i; echo $1 and $2; done; IFS=$OLDIFS
c and 3
e and 5

Answer 4

In cases where my tuple definitions are more complex, I prefer to have them in a heredoc:

while IFS=", " read -ra arr; do
  echo "${arr[0]} and ${arr[1]}"
done <<EOM
c, 3
e, 5
EOM

This combines looping over lines of a heredoc with splitting the lines at some desired separating character.

Answer 5

do echo $key $value
done < file_discriptor

for example:

$ while read key value; do echo $key $value ;done <<EOF
> c 3
> e 5
> EOF
c 3
e 5

$ echo -e 'c 3\ne 5' > file

$ while read key value; do echo $key $value ;done <file
c 3
e 5

$ echo -e 'c,3\ne,5' > file

$ while IFS=, read key value; do echo $key $value ;done <file
c 3
e 5

Answer 6

Based on the answer given by @eduardo-ivanec without setting/resetting the IFS, one could simply do:

for i in "c 3" "e 5"
do
    set -- $i
    echo $1 and $2
done

The output:

c and 3
e and 5