I need to split a line with two string separated by an space like: key value.

I've tried:

key=$(awk -FS=" " print $1 line)
value=$(awk -FS=" " print $2 line)

But I'm getting:

awk: line 2: missing } near end of file

Any ideas?

An awk script on the command line should be single quoted:

awk -F ' ' ' print $1 ' filename

Notice the single quotes around ... , and also that the correct way to set FS is through -F, or through -v FS=... or in a BEGIN block, but not with -FS=....

Your command, the way you have written it, also assumes that line is a file name.

If $line is a string with a single space in it, you can separate it into two strings with

first_part=$line% * # removes the space and everything after it
second_part=$line#* # removes the space and everything before it

Likewise, if $line is a string with a = in it:

first_part=$line%=* # removes the = and everything after it
second_part=$line#*= # removes the = and everything before it

You can also use an array for splitting a line on spaces:

if line is a string

 arr=($line)
 key="$arr[0]"
 value="$arr[1]"

Note:- If the first word of $line is * then the arr array will contain
all the filenames in the current directory. So to be on the safe side and avoid such situations , use

set -f; arr=($line); set +f
key="$arr[0]"
value="$arr[1]"

If line is file

while read -r words
do
 set -- $words
 key=$1
 value=$2
done < line

You can easily achieve this, without using awk, that is inteded for more complex data manipulation.
cut bash command is all you need.

key="$(echo "$line" | cut -d ' ' -f 1)"
value="$(echo "$line" | cut -d ' ' -f 2)"

Hope it helped.

You can use the shell's parameter expansion facilities instead of calling out to an external program:

key=$line%% * # from the end remove the longest string matching
 # a space followed by any characters

value=$line#* # from the start remove the shortest string matching
 # any characters followed by a space

read

Just use read:

read key value

Everything before the first space on the line goes into key and everything after it (including any additional spaces) goes into value.