echo "-123 +1234" | grep -Po '(?<=-)123 (?<=+)1234'

echo "-123 +1234" | grep -Po '(?<=-)123

123 1234

$ echo "-123 +1234" | grep -Po 'd+'
123
1234

$ echo "-123 +1234" | perl -nle'@m=/d+/g; print "@m" if @m'
123 1234

$ echo "-123 +1234" | perl -nle'print "$1 $2" if /-(d+) +(d+)/'
123 1234

echo "-123 +1234" | perl -wnE'@m = /([0-9]+)/g; say for @m'

echo "-123 +1234" | perl -wnE'@m = /(?<=[+-])([0-9]+)/g; say for @m'

echo "-123 +1234" | perl -wnE'@m = /[+-]([0-9]+)/g; say for @m'

echo '-123 +1234 456' | grep -oP '(?<=-|+)d+'
123
1234

echo '-123 +1234 456' | grep -Eo 'b[0-9]+b'