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## Compare symlink to target:

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#

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#   link_check $lnk $tgt && do_link $lnk $tgt || ...

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#

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# Tests if the symlink exists, and the target matches.

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# Fails if the symlink needs updating.

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function link_check {

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    local out="$1"

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    local lnk="$2"

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    [ -e "$out" ] || return 1

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    [ -L "$out" ] || fail "$out: is not a link"

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    [ "$(readlink "$out")" == "$lnk" ] || return 1

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    return 0

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}

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## Update symlink to point to target:

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#

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#   do_link $lnk $tgt

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#

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function link_apply {

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    local out="$1"

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    local lnk="$2"

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    cmd ln -srf "$lnk" "$out"

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    [ -e "$out" ] || fail "$out: given target does not exist: $lnk"

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}

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# Create symlink if not exists.

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function apply_link {

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    local out="$1"

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    local lnk="$2"

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    if link_check "$out" "$lnk"; then

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        log_skip "$out: not changed: $lnk"

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    elif [ "$APPLY" = 0 ]; then

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        log_noop "$out: skip link: $tgt"

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    else

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        log_apply "$out: $tgt..."

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        link_apply "$out" "$lnk"

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    fi

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}