Pick Your Poison :)

awk, via field separators
    awk -F- 'BEGIN {OFS="-"} /id: / { NF=NF-1; match($0,"id: (.*)",a);print a[1]}' /usr/share/haskell/*/register.sh

    That Which Does Not Work
        * negative length considered zero
        awk '/id: / {print substr($2,0,-34)}' */register.sh

bash
    a=$(grep "id: " /usr/share/haskell/haskell-utf8-string/register.sh); a=${a%-*}; a=${a#id: }; echo $a
    a=$(grep "id: " /usr/share/haskell/haskell-utf8-string/register.sh); a=${a%-[[:alnum:]]*}; a=${a#id: }; echo $a

head/tail
    grep "id: " haskell-utf8-string/register.sh | head -c -34 | tail -c +5
    That Which Does Not Work
        * Pipe works on combined output
        grep -h "id: " */register.sh | head -c -34 | tail -c +5

egrep
    That Which Does Not Work
        * groups/lookarounds aren't supported
        egrep -oE 'id: (.*)-.*' haskell-utf8-string/register.sh

awk, via regex
    awk '{match($0,"id: (.*)-.*",a); printf a[1]}' haskell-utf8-string/register.sh
    awk '/id: / {match($2,"(.*)-.*",a); print a[1]}' */register.sh

    That Which Does Not Work
        * awk does not support lookaheads

sed, via regex
    sed -n 's#id: \(.*\)-.*#\1#p' /usr/share/haskell/*/register.sh

    That Which Does Not Work
        * sed does not support lookaheads

perl, via regex + lookahead-regex
    perl -ne 'if ($_ =~ m/id: (.*)-.*/){print $1."\n";}' /usr/share/haskell/*/register.sh

    * positive lookahead and lookbehind
    perl -ne 'if ($_ =~ m/(?<=id: )(.*)(?=-.*)/){print $1."\n";}' /usr/share/haskell/*/register.sh




Examples :)

awk, via field separators
    for package in $(awk -F- 'BEGIN {OFS="-"} /id: / { NF=NF-1; match($0,"id: (.*)",a);print a[1]}' /usr/share/haskell/*/register.sh); do echo -e "]\t$package";done

awk, via regex
    for package in /usr/share/haskell/*; do a=$(awk '{match($0,"id: (.*)-.*",a); printf a[1]}' "$package/register.sh"); echo -e "]\t$a"; done
    for package in $(awk '/id: / {match($2,"(.*)-.*",a); print a[1]}' /usr/share/haskell/*/register.sh); do echo -e "]\t$package"; done

bash
    for package in /usr/share/haskell/*; do a=$(grep "id: " "$package/register.sh"); a=${a%-[[:alnum:]]*}; a=${a#id: }; echo -e "]\t$a"; done

perl
    for package in $(perl -ne 'if ($_ =~ m/id: (.*)-.*/){print $1."\n";}' /usr/share/haskell/*/register.sh); do echo -e "]\t$package"; done