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## Generate updated output file from given command's stdout:

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#

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#   do_update $out $BIN/cmd --args

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#

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# Writes output to a temporary .new file, optionally shows a diff of changes, and commits

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# the new version to $out (unless noop'd).

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    local out="$1"

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    local tmp="$out.new"

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    debug "$out"

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    # compare

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    if [ -e "$out" -a -z "$APPLY_DIFF" ]; then

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        debug "  changes:"

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        # terse

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        indent "        " diff --unified=1 "$out" "$tmp" || true

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    fi

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    # deploy

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    if [ "$APPLY" = 0 ]; then

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        # cleanup

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        debug "  no-op"

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        cmd rm "$tmp"

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    else

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        # commit

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        debug "  deploy"

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        cmd mv "$tmp" "$out"

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    fi

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}

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